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View Full Version : My experience with pH: What I did right and wrong


lrhorer
07/22/2017, 01:57 PM
A few months ago I had a distressing experience with pH fluctuations, and I thought I would relate it for those who might want to know. I tried some of the advice in this forum, and unfortunately some of it made things worse. I was also guilty of allowing a bit of panic override my better good judgement.

First of all, let me comment that the first thing many people ask is, "Are you sure the <name your equipment> is accurate. It is a very good question, and anyone who is experiencing sudden perplexing parameter shifts should do is re-calibrate their equipment to known standards. I also recommend using more than one testing method, as sometimes there can be unanticipated environmental effects that skew the readings. Using more than one method (e.g. indicator solutions plus electronic testing, indicator solutions using different base chemicals, etc.) will tend to eliminate systemic errors produced by otherwise superfluous influences.

Secondly, I personally suggest one test as many parameters as one can when one parameter is out of whack. It is not unusual that one water parameter will actively affect other factors, and it may well be the root cause of the issue may have to be addressed differently than directly trying to modify the initial indicator. Temperature, for example, can have both direct and indirect effects on many qualities of water, and getting the temperature back in line may well produce secondary effects that normalize various aspects of water chemistry as the biological processes reach a proper equilibrium.

I am still not certain what the actual cause of the issue was, but here is what I did and what consequently (I presume) happened:

I was having some problems with a rather massive algae bloom in my aquarium (100g). I had a small ball of chaeto that had become huge, and both the filamentous algae and cyanobacteria had virtually obscured everything in the tank that did not move. I removed most of the chaeto and purchased a yellow tang. I added some phos-sorb to one of the filters and did a moderately large water change (25%) followed by 5 gallon water changes every 3 days. I reduced the lighting period by 2 hours. At that time I did not yet have a phosphate test kit on hand, so I don't really kow how high the phospate may or may not have been. Nitrates were a bit high. I also did not have a water hardness kit at that time, but I knew the water was fairy hard. How hard, I later found out. The pH level was consistently above 8.2.

In just a couple of days, the algae started disappearing quite rapidly. I was quite pleased. Having made some changes, I was keeping a fairly close eye on the water chemistry with all the tests I had in hand, and everything was looking both great in magnitude and quite stable. Then one afternoon about 3 days after the last water change, I walking into the room and all my soft corals were wilted and limp. I immediately checked everything I could, and the only parameter out of whack was the pH, at 7.8 by the chemistry test. I did not have a pH meter. I had bought one, but it was defective, and the replacement had not arrived.

I immediately the recommended dose of pH 8.3, and the pH rose a bit, but then quickly dropped back to 7.8. This continued for several days, until the new pH meter arrived. Although it read the same as the chemical indicator, I was able to see changes more on a real-time basis, and of course more accurately. I kept adding more and more buffer, but no matter what, the pH would always rise for a few minutes and then plummet back to between 7.8 and 7.9. Obviously, something was buffering the water to around 7.8, but I had no idea what. All of the fish were feeling a bit poorly, not eating very well. The soft corals would recover a bit, but then droop again when the pH fell below 8.0.

One of the first things I read here was the suggestion it could be excessive atmospheric C02. I did not see how, since this is a fairly large house and only two of us live here with 2 cats and a Shi Tzu, but I ordered a CO2 scrubber,, anyway. What's more, it is an older house, so it is not sealed tight like some more modern houses. The room itself is fairly large (~ 400 sq ft), adn I am the only one who stayes in it for any length of time. I increased the aeration while waiting for the scrubber to arrive from Europe. There was no noticeable change.

Realizing the 8.3 buffer contained both basic and acidic components, I decided to switch from it to pure NaHCO3. When dosing either the 8.3 buffer or the baking soda, I mixed the powder with a liter of water from the tank before introducing it into the sump. I noticed a fairly significant amount of precipitates formed when mixing the solution. I took it to merely be an artifact of common ions in the aquarium water. I should have paid better attention.

The NaHCO3 did a better job of raising he pH above 8.0 for a few minutes, but then the pH would plummet below 7.9 again. Once more, I should have been paying better attention to what the water was telling me, and to the fact that even though I had instituted two more 25% water changes, the pH level remained intractably low.

The pH meter arrived.

While I was able to monitor the pH level more accurately and continuously than the indicator solution kit, but the effects in the tank remained the same. Then one time when I was dosing the tank with NaHCO3, I noticed some white precipitate forming on the glass of the aquarium. Again, I should have paid more attention. After another dose, the pH nose dived to 7.5, and adding NaCO3 had no effect. A large amount of white precipitate obscured most of front of the tank. I did a massive 50% water change, to no effect. The Colt corals died. The fish were all hiding, and I supposed at least some were dead, although I found no bodies.

I finally got it through my head the water was essentially too hard. I had never considered such a thing to be possible, but it seems to have been the case, and the precipitate was probably mostly CaCO3, with the water being supersaturated with NaHCO3 and some acid - probably sodium tetraborate - buffering the water to 7.5.

I started carefully dosing the tank with 15ml of a 10% solution of NaOH. The pH would rise between .03 and .04 and then fall back about .02, slowly inching upward. I continued dosing every couple of hours. When the pH rose above 8.1 and stayed there, the fish all started coming out and swimming around. Soon they began to eat voraciously. I did not lose a single fish, thank goodness. The crustaceans and molluscs all seem to have come through just fine, although there are too many tiny snails and crabs in the tank to be sure I didn't lose a handful. I dropped the dosage to 10ml and then to 5ml when the pH rose above 8.2 and stayed there. I stopped altogether when the tank stabilized right around 8.25, dropping to about 8.22 at night and peaking at about 8.29 during the day.

Along the way the CO2 scrubber came in, and while it did raise the pH by a few hundredths, the effect was not huge, so I think I am correct in discounting atmospheric CO2 as the principle contributor. I scaled back the water changes to 5 gallons a week. I was buying my water ready-mixed from the LFS. When I obtained a water hardness test, I checked on the aquarium water, and it was completely hard, never changing color at all. I confirmed by mixing the aquarium water 50% with distilled water. The hardness of the resulting solution measured 7. I checked the water from the LFS, and it measures 11. The hardness of untreated water from one of my outside hydrants also measures 11. I have a whole-house water softener, however, and the output from my sink faucet is under 1. I am now using water from my faucet to top off the sump.

Interestingly enough, while the pH remained very stable around 8.25 for several weeks, one night it began rising quite inexplicably. Eventually it topped off at 8.45, which is too high for my comfort, but the only inhabitant that seemed to mind much was the Sea Apple and the one LPS I have in the tank. Having had one bad experience, I was shy of trying to mess with moree chemicals in the tank, but I did not think it would be healthy for the tank to remain that high for long. I removed the CO2 scrubber and added 5ml of white vinegar. This helped, but once again it was not stable. The pH would always rise after a while. I stopped dosing with vinegar, and instead made up some carbonated water. This I dosed at 40ml as long as the pH remained above 8.25. Eventually it stabilized, but every now and then it still goes above 8.3, at which point I remove the CO2 scrubber and if the pH does not fall below 8.3 after a few hours, I dose with 20ml of carbonated water.

bertoni
07/22/2017, 07:08 PM
Just to clarify the chemistry, carbon dioxide (not necessarily from the air) is always the cause of low pH in a running system, assuming nothing strange is being dosed and the alkalinity is in the recommended range:

http://reefkeeping.com/issues/2004-09/rhf/index.htm

Scrubbers often fail to raise pH. The atmosphere is only one source of carbon dioxide. Fish respiration is another big source. Also, scrubbing all the air that reaches an aquarium usually is impractical, since it would require scrubbing the entire room. People often scrub the air going into the skimmer, which can help, but it's also possible for aeration through the tank surface to dominate the carbon dioxide level of the system.

outssider
07/22/2017, 07:18 PM
you my friend are messing around waaaaayyyyyy to much....

first of all....ph is a function of co2 in the tank,usually the room has excess co2, but in your case that seems unlikely. trying to use buffers to change ph is a fools game. what you need to pay attention to is the alkalinity -dkh not ph. I measure ph maybe once a year...at most...and it's always around 8. I dose buffer (sodium bicarbonate) on a systematic basis, the same amount daily along with calcium chloride and magnesium supplements.

don't top off with tap water, you don't know what bad stuff may be in it...always use ro/di for top off and new salt water.

always dissolve your alkalinity/calcium/mag supplement in ro/di water not tank water.

You really need to do some research on reef chemistry because it sounds like you need lots of help....

lrhorer
07/23/2017, 09:26 AM
Just to clarify the chemistry, carbon dioxide (not necessarily from the air) is always the cause of low pH in a running system, assuming nothing strange is being dosed and the alkalinity is in the recommended range:
That is the entire point. Alkalinity was not in the recommended range.

Scrubbers often fail to raise pH. The atmosphere is only source of carbon dioxide.
I think you meant "not the only source". Of course it isn't.

Fish respiration is another big source.
It is if one has a lot of respiration biomass. I don't, really. In fact I suspect the plant matter I removed may have represented more respiration than the animals in the tank.

I had:

1 medium sized Yellow Tang (4 in)
4 Bar Gobies (4-1/2 in)
2 Damsels (1-1/2 in)
1 small Watchman Goby (2 in)
3 Fire Gobies (2-1/2 in)
1 adult Molly (3 in)
4 baby Mollies (1/4 in)

1 Camel Shrimp (1-1/4 in)
1 Banded Coral Shrimp (2 in)
4 Blood Red Fire Shrimp (1-1/2 in)
1 Skunk Cleaner Shrimp (2 in)
10 Peppermint Shrimp (1 in)
2 Horseshoe Crabs (2 in)
1 Emerald Crab (2 in)
1 Sally Lightfoot Crab (1/2 in)
~15 Blue & Red Leg Hermit Crabs (1/4 in)

1 Sea Apple (4 in)
2 Turbo Snails (2 in)
~10 Nassarius Snails (1/2 in)
~10 Bumblebee Snails (1/4 in)
4 Cerith Snails (1/2 in)
2 Tiger Cowries (3-1/2 in)
2 Chestnut Cowries (1-1/4 in)
2 Blue Tuxedo Urchins (1-1/2 & 2 in)
1 White Pincushion Urchin (1 in)

1 Spiny Oyster (5 in)

2 Featherduster Worms (?)
A handful of small sessile invertibrates

Now, even assuming the invertebrates respire as much as the vertebrates (which they do not), that is about 94 inches of fauna biomass. A bit high for a marine aquarium, but not ridiculously so, provided sufficient additional aeration and nitrification are provided. A more realistic estimation is probably about 60 inches of fish equivalents or less, allowing for the crustaceans to have about 1/2 the respiration of a free-swimming fish and the molluscs and the other non-sessile invertebrates about 1/3.

Also, scrubbing all the air that reaches an aquarium usually is impractical, since it would require scrubbing the entire room. People often scrub the air going into the skimmer, which can help, but it's also possible for aeration through the tank surface to dominate the carbon dioxide level of the system.

Not if the tank has a close fitting acrylic top, as mine does. The transpiration of gasses in the aquarium itself is limited by the open surface area of the top, which is less than 25 square cm, in my case. The two largest areas of gas transfer in my system are the skimmer and the wet / dry sump, in that order, confirmed by calculation and by empirical measurements.

More to the point, really, is before the event the pH was stable right around 8.25, and now it is fairly stable around 8.3, with occasional excursions as high as 8.42. When that happens, I have to add CO2, not reduce it. There is virtually no way to reconcile the fact with high levels of CO2 in the room.

lrhorer
07/23/2017, 11:00 AM
you my friend are messing around waaaaayyyyyy to much....
I admitted I was doing so during the event. Not before or after. Once the tank had cycled, I was doing almost nothing but water changes, feeding, and occasionally stirring the substrate. All I did proximate to the event was a 25% water change, the addition of a little bit of phos-sorb into one of the filters, removing the ball of chaeto, and reducing the lighting a bit, followed by a few ordinary small water changes, all over a period of a few weeks.

Since then, all I have done is add a weak acid (at first vinegar but now just plain dissolved CO2) whenever the pH rises above 8.4, as it does upon occasion. I have not suffered any dips below 8.2 pH since the problem was resolved.

first of all....ph is a function of co2 in the tank,usually the room has excess co2
Not to be pedantic, but it is a function of all the chemicals in the water, even NaCl. Although a pure solution of NaCl in H2O is supposed to be 7.0, in practice it is generally not, admittedly usually because of the presence of CO2. I suspect the Marine Buffer I was using had Sodium Tetraborate and Boric Acid as components. In any case, the fact was adding NaHCO3 to the water caused the pH to plummet, and this can only happen if the solution is saturated with carbonate ions and some common ion is causing the H+ concentration to drop. It is unquestionable the hardness of the tank was off the scale. Only supersaturation of carbonate ions could result in the massive precipitation of NaHCO3 and or CaHCO3 that happened in the tank. That, plus the measured hardness of the tank itself was off the scale, and the measured hardness of the seawater I was using to replenish the tank was 11.

All that said, I do suspect, but cannot prove, the original cause of the pH drop was the production of CO2 by the die off of large amounts of vegetation in the tank. This I suspect was followed by the saturation of B4Na2O7 and NaHCO3 along with whatever chemicals the manufacturer of the buffer uses to prevent the pH of the treated solution from rising above 8.3.

If you have a better explanation how adding NaHCO3 to a solution can lower its pH well below 8, I am listening.

but in your case that seems unlikely. trying to use buffers to change ph is a fools game. what you need to pay attention to is the alkalinity -dkh not ph.
Since I did not at the time have a carbonate hardness test, that was not an option. Right now it is at 10.

I measure ph maybe once a year...at most...and it's always around 8. I dose buffer (sodium bicarbonate) on a systematic basis
Yes, but remember in this case dosing with CaHCO3 eventually caused the pH to plummet to 7.5, and large amounts of precipitate to form. By running a glass scrubber over the aquarium front a couple of minutes every day, I have been able to get rid of most of it. As you can see from the attachment, there is some particularly stubborn scale still left in one quadrant of the front glass.

don't top off with tap water, you don't know what bad stuff may be in it...always use ro/di for top off and new salt water.
Your point is taken, and indeed I have been thinking about possibly getting a RODI filter. The problem right now is I am really strapped for cash. I had several thousand dollars of unexpected expenses hit.

One LFS sells DI water, the other (whose pre-mixed sea water has a hardness of 11) sells RO water. I just measured the hardness of the DI water: it's 2. I don't have a sample of the other store's RO water.

always dissolve your alkalinity/calcium/mag supplement in ro/di water not tank water.
Yes, although if the salt water is not well balanced, an easy indication of water that may be too hard is the production of precipitate when adding small amounts of supplement to a 1 liter sample of the tank water.

You really need to do some research on reef chemistry because it sounds like you need lots of help....
Not so much, I think. I have done a fair amount of research in the last 30 years that I have owned saltwater tanks, and particularly in the past nine months that I have been converting my unused 100g to a reef tank. On the other hand, I never stop researching anything with which I am involved. Yet while I am a physicist and engineer, rather than a chemist, I do know a fair bit about inorganic chemistry. I have no doubt, of course, you and others on this forum may well know a great deal more.

bertoni
07/23/2017, 05:13 PM
That is the entire point. Alkalinity was not in the recommended range.


I think you meant "not the only source". Of course it isn't.

Yes, that was a typo. I should go back and fix it.


It is if one has a lot of respiration biomass. I don't, really. In fact I suspect the plant matter I removed may have represented more respiration than the animals in the tank.

I had:

1 medium sized Yellow Tang (4 in)
4 Bar Gobies (4-1/2 in)
2 Damsels (1-1/2 in)
1 small Watchman Goby (2 in)
3 Fire Gobies (2-1/2 in)
1 adult Molly (3 in)
4 baby Mollies (1/4 in)

I would call that a heavy load for a 100g system, but opinions vary. I would have stopped at around half that, but opinions also vary there.

Not if the tank has a close fitting acrylic top, as mine does. The transpiration of gasses in the aquarium itself is limited by the open surface area of the top, which is less than 25 square cm, in my case. The two largest areas of gas transfer in my system are the skimmer and the wet / dry sump, in that order, confirmed by calculation and by empirical measurements.
I agree that your system probably had a small effect, if any, from carbon dioxide in the air. I would say the issue was a fairly high fish load, possibly with a low alkalinity level, and also possible aeration limitations. A tight-fitting lid could trap a lot of carbon dioxide, although that can vary, too, depending on how tight the fit actually is. You didn't give any clear indications of the alkalinity level of the tank, only the pH, so I don't know what influence that might have had.

bertoni
07/23/2017, 05:18 PM
I
Not to be pedantic, but it is a function of all the chemicals in the water, even NaCl. Although a pure solution of NaCl in H2O is supposed to be 7.0, in practice it is generally not, admittedly usually because of the presence of CO2.
The pH of saltwater is determined by the alkalinity and the amount of carbon dioxide dissolved in it:

http://reefkeeping.com/issues/2004-09/rhf/index.htm

NaCl is a neutral salt, and a pure solution will have a pH of 7. Adding carbon dioxide to the mix will drop the pH, but neutral salts don't affect the pH. Google turns up a lot of references.

lrhorer
07/24/2017, 03:22 AM
I agree that your system probably had a small effect, if any, from carbon dioxide in the air. I would say the issue was a fairly high fish load, possibly with a low alkalinity level
No, it was supersaturated with carbonates. Higher than high.

and also possible aeration limitations.
It's pretty well aerated. The skimmer moves a high volume of air, and the sump produces a pretty good aeration. I forgot to mention one of the first things I tried was adding an air stone to the sump. It produced no measurable effect.

A tight-fitting lid could trap a lot of carbon dioxide, although that can vary, too, depending on how tight the fit actually is.
The fit is tight, but as I mentioned there is still about 25 square cm or so of venting around the various pipes and power cords, plus the sump cavity is open to the air. Not only that, but merely opening the two tank lids would immediately dissipate any significant excess of CO2, and I did that a lot. I keep the lids shut when I am not there, because a number of the residents are jumpers, but I am not shy about keeping them open when I am there.

You didn't give any clear indications of the alkalinity level of the tank, only the pH, so I don't know what influence that might have had.
Well, I thought I mentioned it. When I received the alkalinity kit, the alkalinity of the tank was off the scale. The only way to get a change from the indicator solution was to mix the tank water 1/2 and 1/2 with distilled water. The result was a dKH of 7. I verified the distilled water had a dKH of less than 1. The alkalinity of the seawater from the LFS is 11. That''s why some pretty major water changes didn't resolve the issue. Clearly, no precipitate can ever form from any aqueous solution unless it is supersaturated, and a TON of carbonate precipitated from solution in the tank. That is also why significant doses of NaOH eventually cleared the issue, and why the addition of NaHCo3 actually caused the pH to drop precipitously. In short, the water was about as hard with carbonates as solid marble.

I see no way to reconcile the idea the problem was caused by a high fish load with the fact that now the pH is persistently high with a dKH of 10, even though most of the algae is gone, and there are no fewer fish than before. With no dosing whatsoever, the pH occasionally rises to 8.45. It has been dark for several hours, and the pH is still at a very respectable 8.33.

No, the fact is supersaturated solutions work differently than normal molar solutions, especially when the common ion effect is in play.

lrhorer
07/24/2017, 04:21 AM
The pH of saltwater is determined by the alkalinity and the amount of carbon dioxide dissolved in it:
This assumes:
1. No other acids are present in significant amounts
2. No basic ionic solids are present in significant amounts other than carbonates
3. None of the ionic solids are saturated.
4. Common ions are in comparatively low concentrations.

NaCl is a neutral salt, and a pure solution will have a pH of 7.
Correct. There is, however, no such thing as a pure solution, even in a laboratory. To prepare anything close to a pure aqueous solution of H2O + NaC, one must prepare it in an atmosphere consisting of only inert gases.

Adding carbon dioxide to the mix will drop the pH, but neutral salts don't affect the pH. Google turns up a lot of references.
Actually, it definitely can. If CO2 is the only dissolved ionic substance in a solution, then it is true adding reasonable amounts of NaCl will not have much effect on the pH of the solution. If, however, a buffered solution contains sub-saturated amounts of an acid and / or its conjugate base, then adding any ionic solid containing any component of either solute will not only change the pH of the solution but also will reduce the solubility of the solid containing the common ion. The SeaChem 8.3 buffer does not specify exactly what the components of the buffer are, but it certainly does contain sodium bicarbonate and some forms of borate, including I suspect boric acid and sodium tertraborate. Plenty of common ions there, including Na+, H+, and CO3--. Boric acid also has 3 OH- groups which readily increase the pOH of the solution, thereby decreasing the pH. I suspect it is this which caused the pH to plummet once the carbonates had reached saturation levels.

As to what caused the initial precipitous drop in pH, I am not sure, but my best guess would be copius amounts of CO2 and other acids produced by the large scale decay of plant matter as the Algae in the tank died off. I can't think of anything else that suddenly changed. At first one might think it was due to the reduction of photosynthesis caused by the removal of a large amount of live plant material, but that does not track, because now the die-off has tapered, the pH is not low even though the fish load is the same as before. Fish loading and atmospheric CO2 concentrations cannot have been responsible, since they did not change at any point. Water hardness might have changed with the water changes, but with a dKH of 11 in the replacement seawater, I don't see how it could have come down, and in any case the current hardness of 10 is more than enough to maintain a pH higher than 8.2 in the system.

bertoni
07/24/2017, 06:11 PM
No, it was supersaturated with carbonates. Higher than high.

I thought you implied that the tank was low in alkalinity. It can't both be low in alkalinity and high in carbonate. Also, "saturated" doesn't have much meaning here. Do you mean supersaturated with respect to calcium carbonate? What was the alkalinity level?

The fit is tight, but as I mentioned there is still about 25 square cm or so of venting around the various pipes and power cords, plus the sump cavity is open to the air. Not only that, but merely opening the two tank lids would immediately dissipate any significant excess of CO2, and I did that a lot. I keep the lids shut when I am not there, because a number of the residents are jumpers, but I am not shy about keeping them open when I am there.
I can't judge the airflow from the room over the top of your tank, so you might be quite right about the carbon dioxide level over the system.

Well, I thought I mentioned it. When I received the alkalinity kit, the alkalinity of the tank was off the scale. The only way to get a change from the indicator solution was to mix the tank water 1/2 and 1/2 with distilled water. The result was a dKH of 7. I verified the distilled water had a dKH of less than 1. The alkalinity of the seawater from the LFS is 11. That''s why some pretty major water changes didn't resolve the issue. Clearly, no precipitate can ever form from any aqueous solution unless it is supersaturated, and a TON of carbonate precipitated from solution in the tank. That is also why significant doses of NaOH eventually cleared the issue, and why the addition of NaHCo3 actually caused the pH to drop precipitously. In short, the water was about as hard with carbonates as solid marble.
A very high alkalinity level is consistent with using buffers to control pH. Lots of people have that issue. High-pH buffers work essentially by consuming carbon dioxide from the water, so the effect is temporary in nature.

I see no way to reconcile the idea the problem was caused by a high fish load with the fact that now the pH is persistently high with a dKH of 10, even though most of the algae is gone, and there are no fewer fish than before. With no dosing whatsoever, the pH occasionally rises to 8.45. It has been dark for several hours, and the pH is still at a very respectable 8.33.
I agree that something has been fixed, but your description is a bit vague, so I can't be sure which. My initial thought was that the alkalinity level had gotten low. That combined with aeration issues of some sort could cause this type of problem, but there's not enough data in your post for me to be sure.

No, the fact is supersaturated solutions work differently than normal molar solutions, especially when the common ion effect is in play.
Saltwater is supersaturated with respect to calcium carbonate. I don't see how this play into any interesting pH effect other than the alkalinity level obviously is higher.

duncanpate1
07/24/2017, 06:21 PM
What's PH?
( tongue in cheek)


Sent from my iPhone using Tapatalk

bertoni
07/24/2017, 06:27 PM
This assumes:
1. No other acids are present in significant amounts
2. No basic ionic solids are present in significant amounts other than carbonates
3. None of the ionic solids are saturated.
4. Common ions are in comparatively low concentrations.

I'm not sure what acid would be prevalent enough in a running system (after any large decay process) to make a notable difference. This article covers buffering in seawater:

http://www.advancedaquarist.com/2002/2/chemistry

In order for it to be seawater, it needs to meet some basic criteria as to what's in it. You are correct that some of the buffer products add forms of borate or other compounds containing boron. That was on the labels of at least some of them at some point. The one you mentioned likely does, as well, although I haven't seen the label. I'm not sure what point you are trying to make. Certainly, if we tamper with the ratios of ions in the water significantly, we can change the pH, but at some point, I'd have a hard time calling it "seawater", and I don't think any of the manipulations you've mentioned will do all that much. There might be a significant amount of borate in the mix, but that seldom seems to accomplish much in reality. A shift of 0.1 to 0.2 pH units is about the most I've seen claimed on paper, with most people not reporting much of a change at all.

Actually, it definitely can...
All of the examples you mentioned are part of the alkalinity of the system, and none are neutral salts. At some point, adding neutral salts could cause pH changes, by causing precipitation, as one case, but that's not a situation that occurs in a reef tank unless someone makes a large mistake. The solution there is to replace the water column. I must admit I am not overly concerned with nor am I considering chemistry beyond what is reasonable to assume is happening in our tanks. This forum is about reef chemistry, and when this type of conversation starts, I probably should start qualifying my answers, as a reminder to everyone reading the thread.

As to what caused the initial precipitous drop in pH, I am not sure, but my best guess would be copius amounts of CO2 and other acids produced by the large scale decay of plant matter as the Algae in the tank died off. I can't think of anything else that suddenly changed. At first one might think it was due to the reduction of photosynthesis caused by the removal of a large amount of live plant material, but that does not track, because now the die-off has tapered, the pH is not low even though the fish load is the same as before. Fish loading and atmospheric CO2 concentrations cannot have been responsible, since they did not change at any point. Water hardness might have changed with the water changes, but with a dKH of 11 in the replacement seawater, I don't see how it could have come down, and in any case the current hardness of 10 is more than enough to maintain a pH higher than 8.2 in the system.
I agree that a dKH of 10 is a fine level for a tank. Carbon dioxide or decay could make the pH very low, as you state, but you were the only witness to the changes in your tank, so we can't help much there.

lrhorer
07/24/2017, 08:16 PM
I thought you implied that the tank was low in alkalinity.
No, not at all. When the event began, I had no way of knowing exactly what the alkalinity was, since I did not have a carbonate hardness test. All I knew was that after several months of being steady, in a matter of hours the pH dropped from around 8.2 to 7.8. Nothing at all was done to the tank other than feeding and topping off via an ATO in the 3 days prior to the event, but the amount of algae was steadily and rapidly decreasing.

It can't both be low in alkalinity and high in carbonate.
Of course not. As I said, at the outset of the event, I did not have a carbonate hardness test, so I don't really know what the hardness was. Since the water I was using to do the water change was eventually tested and found to have a dKH of 11, and since the tank quickly saturated with at least one of the buffer reagents, I must presume it to have been reasonably high.

Also, "saturated" doesn't have much meaning here. Do you mean supersaturated with respect to calcium carbonate?
I have no way of knowing with certainty. The only data I have is the fact addition of NaHCO3 produced large amounts of precipitates. That suggests high carbonates, but without an actual chemical analysis of the water and / or the precipitates, I have no way of being certain. Clearly something was buffering the water, as nothing I did would budge the pH away from first 7.8 and then later 7.5 pH. Furthermore, the fact adding either NaHCO3 or NaOH both resulted in a precipitate strongly suggests the system was saturated with carbonates, since adding NaHCO3 to a saturated solution will directly precipitate NaHCO3 and adding NaOH to a system containing dissolved CO2 will produce both NaHCO3 (Sodium Bicarbonate) and Na2CO3 (Sodium Carbonate). One or both of these are almost surely to be among the precipitates.

What was the alkalinity level?
Once again, I have no way of knowing what it was at the outset of the event. Once I received the hardness kit, it was off the scale. That is after I began dosing with NaOH, which is what eventually resolved the issue. It was too late for the soft corals, but everyone else bounced back nicely.

I can't judge the airflow from the room over the top of your tank, so you might be quite right about the carbon dioxide level over the system.
The fact the pH peaks at 8.45 with a dKH of 10, no CO2 scrubber, and no other change to the apparatus would suggest CO2 is not a problem. The airflow over the tank water is pretty low, but not zero, so it would not be expected to trap much CO2.

A very high alkalinity level is consistent with using buffers to control pH. Lots of people have that issue. High-pH buffers work essentially by consuming carbon dioxide from the water, so the effect is temporary in nature.
Yes, but "temporary" is a relative term. It was more than long enough to kill the soft corals and make the fish rather sick.

I agree that something has been fixed, but your description is a bit vague, so I can't be sure which. My initial thought was that the alkalinity level had gotten low. That combined with aeration issues of some sort could cause this type of problem
Yes, but in that case adding NaHCO3 would not have caused the pH to plummet, rather than rise, and the tank would not have produced very large amounts of precipitate when adding the NaHCO3. The carbonate hardness also would not have read off the chart (>12), when the kit did come in. Finally, the large scale addition (well over 50% in all) of seawater with a dKH of 11 would have quickly resolved - indeed prevented - the issue if it were related strictly to low hardness.

The bottom line is this:
1. I can think of no process or activity in the tank that could have dropped the alkalinity in the tank precipitously in a matter of less than 6 hours.

2. The removal of a large mass of live vegetation certainly was expected to result in an increase in CO2 from animal respiration, but since CO2 levels seem to be quite low once the tank settled, it is not a prime suspect for the main root cause of the event.

3. The salt water used to do the water changes both before and during the event was later found to have a hardness of 11. I see no way this could have contributed to the initial event nor the subsequent drops in pH.

4. I don't think the addition of a small amount of PhosGuard could have of itself caused the drop in pH.

5. The large scale die-off of large amounts of plant life most definitely could have produced a significant increase in CO2. It also can release various acids from the plant tissue and subsequent decay products, including but not limited to Sulphuric acid, Nitric acid, Nitrous acid, and Hydrochloric acid. Why the sudden precipitous drop eludes me, though.

but there's not enough data in your post for me to be sure.
Well, me, either. That is why I strongly suggest everyone test as many water parameters as they can during a precipitous event, including Carbonate hardness, pH, Nitrates, Phosphates, ORP, specific gravity, temperature, and Calcium. It won't hurt to test Ammonia and Nitrite, either. Had I been able to do so, I believe I could have saved my soft corals and reduced the stress to my fish.


Saltwater is supersaturated with respect to calcium carbonate. I don't see how this play into any interesting pH effect other than the alkalinity level obviously is higher.[/QUOTE]

bertoni
07/24/2017, 09:20 PM
An alkalinity drop usually happens only when calcium carbonate precipitates, along with some magnesium in the mix. Such precipitation events can remove a lot of alkalinity in a few hours.

Adding sodium bicarbonate should drop the pH a bit when initially added (in most, maybe all, circumstances), because it adds carbon dioxide to the water column. This usually very small drop will be followed by a rise when carbon dioxide outgasses. The amount of the drop and the rise would depend on the alkalinity of the system at the time.

PhosGuard might be capable of triggering precipitation. Phosphate is part of the buffer, although generally a tiny one, but more importantly, the surface of such phosphate absorbers often is a precipitation site. This article covers GFO, but the effect might be similar:

http://reefkeeping.com/issues/2004-11/rhf/index.htm

I suspect that you are correct, though, and the PhosGuard had little or no effect.

gprdypoo04
07/24/2017, 11:01 PM
Yawn......

Mishri
07/25/2017, 10:39 AM
so.. what I got from this was OP didn't run all of the recommended tests-too focused on ph.. did a bunch of things that likely messed with his chemistry. and eventually ran the tests he should have.. and now everything is working once he got his parameters back in line.. cool beans.

:beer:

lrhorer
08/05/2017, 07:58 PM
See the next thread.

duncanpate1
08/05/2017, 08:33 PM
Chasing PH is a fools errand!!!


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lrhorer
08/06/2017, 04:20 PM
So what else should I do? Again, see the next thread. The livestock was suddenly stressed and some were obviously dying. Hardness, specific gravity, Ammonia, Nitrite, and Nitrate were all optimal or near perfect. Today the pH is much more normal, and the livestock are less stressed. Should I have simply let them all die because you think, "Chasing pH is a fool's errand"? Adding CO2 was effective. What is your suggestion?

No offense intended, but I request if you or others cannot provide positive, helpful advice to those of us who seek genuine enlightenment, please say nothing at all. Snarky comments only add noise to the forum.

Lsufan
08/06/2017, 10:45 PM
Don't take it the wrong way but I believe some of the comments are because u seem to be arguing with the advice u have gotten. That may not at all be what u are trying to do. my advise would be to listen to bertoni's comments. Bertoni is one of the most knowledgeable people on the board & if he says something as fact then it is fact. If he isn't quite sure how something may react or if there is no way to know how something may react he will say so, but he won't say something as fact if it isn't.

I don't know 2% of what bertoni does & I know u didn't want to hear what mishri posted but that is probably what most people who read this thread thought. Alkalinity is the most important test followed by calcium & mag. It sounds likely that u had low alk & between that & a couple other factors caused your issues. Adding the ph buffer raised your alkalinity so by the time u tested it it was back up to a good level. I don't know if that was the case but it seems like there is a good chance it was

lrhorer
08/19/2017, 04:21 AM
Don't take it the wrong way but I believe some of the comments are because u seem to be arguing with the advice u have gotten.
Advice is not relevant. I thought I stated clearly his was an event that happened some months ago. The motivation for this thread is to point out that a number of people have reported events that sound very similar to the one I had and were either led down the garden path or insulted, or both.

That may not at all be what u are trying to do.
I am relating a story about some mistakes I made and how I ultimately fixed the issue.

my advise would be to listen to bertoni's comments. Bertoni is one of the most knowledgeable people on the board & if he says something as fact then it is fact.
I always listen to everyone's comments. Furthermore, Bertoni seems to both well experienced and also an urbane, thoughtfull, and helpful individual. I submit he probably deserves high marks all around. Nonetheless, somehow he got the impression I said the dKH was low. I never said any such thing. Although I did not have the ability to measure the alkalinity directly, by concrete inference, we know it was not. Had it been, adding the 8.3 buffer would have raised the pH.

I know u didn't want to hear what mishri posted but that is probably what most people who read this thread thought. Alkalinity is the most important test followed by calcium & mag.
You and he are both missing the point, and all three of you have somehow completely failed to understand what I wrote. Perhaps that is my fault. I will summarize it in three lines:

Alkalinity: Higher than high. Higher than any aqueous solution in equilibrium can be. >12.

Ph: 7.5

CO2: Very, very low

It sounds likely that u had low alk
It sounds like nothing of the sort. The only way it "sounds likely" is if someone assumes without evidence that a low pH means the carbonae hardness must be low or the CO2 must be high, or both. My whole point is this is simply untrue. By rigid inference, the carbonate hardness was above 12.

& between that & a couple other factors caused your issues. Adding the ph buffer raised your alkalinity so by the time u tested it it was back up to a good level.
Then, given the CO2 levels were and are quite low, how is it the pH was at 7.5 when the alkalinity was high?
That ignores the facts as I stated them:

1. More than 50% of the water was replaced with pre-mixed water whose hardness was measured at 11. The pH remained at 7.5.

2. Adding the 8.3 buffer LOWERED the pH from 8.1 to 7.9. Adding additional recommended doses did not raise the pH at all. It remained at 7.9 through many dosing cycles.

3. At this point, precipitates started to form. No precipitate can form in any solution unless the solution is saturated with the precipitate. Ever. Translation: the water was as hard as the 8.3 buffer could ever make it.

4. I switched to NaCO3. The pH dropped to 7.9 and stayed there, again through many dosing cycles. Precipitation of carbonates was so heavy almost the entire front of the aquarium turned opaque white with a heavy layer of hard precipitate.

5. I switched to NaOH, which is what I should have done from the start.

I don't know if that was the case but it seems like there is a good chance it was
It most definitely was not, because the dKH was never low.

ssgss gogeta
08/19/2017, 04:47 AM
I'm new to this forum and I've also joined a Facebook page (both this forum and the Facebook page seem to be predominant of American and Canadians) and I am Australian. The interesting thing I have noticed more so on the Facebook page (just quietly the larger amount of stupidity on the Facebook page compared to general knowledgeable people on this forum) the severe care for ph. The way I was taught to reef originally many years ago was ph super important. Then it was keeping alkalinity, calcium, mag, salinity, oxygen and temperature were the main things alongside nitrate and phosphate. And ph was something we just completely forgot about and nothing bad happened and the way it was explained to me was simply that if my alk and oxygen was stable and fine than ph would never be an issue. And to run my thoughts around in circles again mostly on the Facebook page I see people chasing a ph and doing all these crazy things.

Long story short ph is obsolete at least in my local circles and on the interwebz I've been seeing a lot of craziness in chasing a ph and probably throwing everything else out of wack in the process


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lrhorer
08/19/2017, 06:32 PM
I'm new to this forum
So am I, but welcome, mate! I would dearly love to visit your magnificent country and dive the Great Barrier Reef. I might not come home.

the severe care for ph. The way I was taught to reef originally many years ago was ph super important.
Well, it is. In aqueous solutions, pH / pOH is the driving force behind the speed with which all ionic reactions occur, or whether they occur at all. The problem, for the aquarium enthusiast, is the pH can suffer wide swings in a very short time due to environmental factors that can and do change on an hourly basis, or even less. The aquarium enthusiast is generally much better suited to try to target more stable metrics so as to provide a metastable environment. Some of the folks here have assumed I did not know this. Why they did so, I have no idea. One should never assume anything, at least not without specifically documenting the assumption. If any proof is incorrect, it is usually because one or more of the postulates is incorrect.

Then it was keeping alkalinity, calcium, mag, salinity, oxygen and temperature were the main things alongside nitrate and phosphate.
O2 also quite normally varies throughout the day, as does CO2. The "trick" if you will, is to try to arrange it so both are continuously near optimal levels throughout the day. The bottom line is one should not be continually messing with the aquarium environment. It is often going to wind up doing more harm than good. This is why focusing on more generally stable parameters is a good idea. What's more, some of them do affect pH, and keeping them in an optimum range will go a long way toward keeping the pH range within tolerable parameters. Note in the wild, the pH is ordinarily much more stable, although even there it fluctuates a little daily. It is one of the parameters we evaluated very closely when I was part of a scientific team evaluating the health of the marine environment and the impacts of certain activities in the Gulf of Mexico.

And ph was something we just completely forgot about and nothing bad happened and the way it was explained to me was simply that if my alk and oxygen was stable and fine than ph would never be an issue.
The first problem is, this is not always true. I submit the second problem is a number of people have it ingrained in their minds it must always be true.

It is about buffering. What is a chemical buffer? It is a substance which, when added to an aqueous solution, prevents the pH of the solution from changing as much when other chemicals are added as much as it would when the same amount of said chemicals are added to pure water. Buffers are usually created by adding a weak acid or a weak base along with one or more of its salts to the initial reagent solution. Then, when an acid or a base, even a strong acid or base, is added to the solution, the pH change is far, far less than that of adding the same amount of the same chemical to pure water. The term "water hardness" is very loosely used to cover a number of quite different situations, but generally speaking, hard water is fairly heavily buffered, and so it has a much more stable pH than pure water.

What that means for the aquarium enthusiast is harder water in general is going to have a much more stable pH. With that in mind, keeping a handle on alkalinity will reduce the swings in pH for a given change in constituent bases and acids, and consequently keeping an eye on dKH will USUALLY, indeed almost always keep pH in line. The problem here is "almost always" is not the same as "always". It would seem many people also fail to realize "in every case I have seen" is not the same as "always", either.

And to run my thoughts around in circles again mostly on the Facebook page I see people chasing a ph and doing all these crazy things.
Back in the 70s, I was having a conversation with an Oceanographer friend whose job was maintaining a large number of marine aquaria for his department in the university. I had one 30g fish-only aquarium in my apartment. When I would come back from sea duty, I would sometimes being back one or two specimens with me. It was often a chore keeping them alive. His response was, "It's really amazing any fish can ever survive in an aquarium." Fortunately, life is pretty tough.

Long story short ph is obsolete at least in my local circles and on the interwebz I've been seeing a lot of craziness in chasing a ph and probably throwing everything else out of wack in the process

Like I did. As I said, I rather panicked, and not having enough of the right chemistry tests to hand, I did the wrong thing. Had I known the hardness was already high, I would never have added more 8.3 buffer. I would have gone straight to vinegar, and then to NaOH as soon as I could get some, which would have been four days. Note the problem as far as the sick fish were concerned was indeed pH, but the root cause was not low alkalinity, as I incorrectly surmised. Basically, I was guilty of the same assumption others here have made: low pH is the result of low alkalinity.

lrhorer
08/19/2017, 06:47 PM
so.. what I got from this was OP didn't run all of the recommended tests-too focused on ph
No, I was not too focused on pH. I simply did not have the tests available to me, nor were they going to be available for several days. No matter how much they are recommended, no one can run tests they do not have available.

.. did a bunch of things that likely messed with his chemistry.
Not likely at all: absolutely certain, although it was not a bunch of things. It was just two, or really just one. I was trying to raise the alkalinity. It was already too high.

and eventually ran the tests he should have.. and now everything is working once he got his parameters back in line.. cool beans.
The other way around. I was able to run the tests after I had already realized the solution. They confirmed what I had already realized.

:beer:
No, thanks, I don't drink.

ssgss gogeta
08/20/2017, 06:38 PM
And I know your probably feeling a bit attacked ATM. But given what you know now would you have all your test equipment ready in the future? I mean and not trying to be a *****. But I have never started a tank without having every important test kit.


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duncanpate1
08/20/2017, 08:32 PM
No, I was not too focused on pH. I simply did not have the tests available to me, nor were they going to be available for several days. No matter how much they are recommended, no one can run tests they do not have available.





Not likely at all: absolutely certain, although it was not a bunch of things. It was just two, or really just one. I was trying to raise the alkalinity. It was already too high.





The other way around. I was able to run the tests after I had already realized the solution. They confirmed what I had already realized.





No, thanks, I don't drink.



Time to start?


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