Low pH from elevated CO2, any cures?

[BrianPlankis]

Randy,

I have a 90 gallon system and I've been using the Salifert pH test kit for almost a year. I always thought my pH was around 8.0-8.2 from the test kit. I started topping off with Kalk (3 gallons in 2-3 days) and the Salifert kit started reading 8.4-8.6!

However, I recently purchased a digital pH pen(properly calibrated twice a month or more) for monitoring my pH and I found that it drops to 7.8 at night and gets up to around 8.1 during the day. This is with adding 3 gallons of kalk every 2-3 days via auto top-off. I also add about 60mL of your 2 part Alk supplement every 2-3 days (Recipe #1 that raises pH)

My Alk drops very fast in my tank (Calcium drops fast too, but slower) at about 1.5 -2 dKH every two days. I suspect because of a light coral load and a very heavy baby snail population

Parameters:
Ca: 380-440ppm
Alk: 7.0 - 10.0 dKH
pH: 7.8-7.9 night, 8.0-8.15 day
Mg: 1200-1300ppm
NH4, NO2, NO3, P04: All zero

I run an ASM G2 skimmer that does a great job of aerating the water. I do not run a Ca reactor.

I did the C02 aeration test and confirmed our house's CO2 is elevated. With Texas heat and humidity it is not possible to open windows except on the occasional cool night after a rain.

I do not have easy access to the outside where the tank is, but I'll look into bringing in fresh outside air through our AC system.

I read your article:
http://www.reefkeeping.com/issues/2004-09/rhf/index.php

However, it appears I'm doing everything I can except for adding fresh air via the skimmer.

The only other thing I can think of is to increase evaporation a little with another fan so I have to add more kalk. As long as my Ca and Alk levels stay in the good range that could work. Do you have any other suggestions?

Brian

[Biggie]

Just posted the same problem earlier today found I have the same situation. I live in FL. and the windows go down and AC goes on after first of May here. My question is, is your stand enclosed all around like mine? I have aeration in my sump where theres no escape for the CO2 even though I have an open top and a fan goin 24-7 its not enough. I monitor with a pinpoint that has a new probe so I know its on the money. I did the aeration test and it was infact high CO2 amazing little tid I got off RC from a guy today. Im moving my aeration top side with some creativity and boosting up my Alk some with more Kalk on a drip and see if that corrects the PH instability Im getting. I go dramatically from 8.3 to 7.8 in 24 hours. Im BB too which is like unheard off. Its a gas exchange issue with me definatley. The stand enclosure is a major contributing factor thats where my aeration take splace to keep the main display bubble free but its gotta change or Ill never get my PH to stabilize. Hope this helps in some fashion.

[BrianPlankis]

<a href=showthread.php?s=&postid=7436371#post7436371 target=_blank>Originally posted</a> by Biggie
Just posted the same problem earlier today found I have the same situation. I live in FL. and the windows go down and AC goes on after first of May here. My question is, is your stand enclosed all around like mine? I have aeration in my sump where theres no escape for the CO2 even though I have an open top and a fan goin 24-7 its not enough. I monitor with a pinpoint that has a new probe so I know its on the money. I did the aeration test and it was infact high CO2 amazing little tid I got off RC from a guy today. Im moving my aeration top side with some creativity and boosting up my Alk some with more Kalk on a drip and see if that corrects the PH instability Im getting. I go dramatically from 8.3 to 7.8 in 24 hours. Im BB too which is like unheard off. Its a gas exchange issue with me definatley. The stand enclosure is a major contributing factor thats where my aeration take splace to keep the main display bubble free but its gotta change or Ill never get my PH to stabilize. Hope this helps in some fashion.

My tank is enclosed on three sides (it is in an alcove designed for a TV). I do have two doors on my stand, but I'm currently keeping those open due to a heat issue. It seems like adding an additional fan to raise evaporation will help my pH problem and heat problem at the same time.

Brian

[Billybeau1]

You could try putting a lamp over your sump and have it on a reverse light cycle. So when your tank lights are off, the sump light is on. This will continue photosynthisis and minimize the ph swing at night.

[BrianPlankis]

<a href=showthread.php?s=&postid=7437250#post7437250 target=_blank>Originally posted</a> by Billybeau1
You could try putting a lamp over your sump and have it on a reverse light cycle. So when your tank lights are off, the sump light is on. This will continue photosynthisis and minimize the ph swing at night.

Good point! I am doing this though. I have a ball of cheato under a 6500K HD light that makes it grow like crazy. It is about time to change that bulb though, so changing the bulb might help as well.

Brian

[Randy Holmes-Farley]

Don't worry about extra limewater from increasing evaporation pushing calcium or alkalinity too high. Raising the pH sometimes has the opposite effect as it increases the demand for calcium and alkalinity by both corals and abiotic precipitation.

So more limewater and/or more fresh air are the options.

What happened when you aerated it? Did you try outside air? Without that confirmation, there is the possibility that the pH measurement is in error.

[BrianPlankis]

<a href=showthread.php?s=&postid=7437945#post7437945 target=_blank>Originally posted</a> by Randy Holmes-Farley
What happened when you aerated it? Did you try outside air? Without that confirmation, there is the possibility that the pH measurement is in error.

Randy,

I don't have the numbers in front of me, but I took a cup of tank water and aerated it using an air pump inside the house and outside the house.

Inside the house the pH only went up like 0.02 or something like that. Outside the house the pH went up by over .20 units(from 8.1x to 8.3x).

I guess I could add 500 plants to the house to increase CO2 consumption? :D

Brian

[Casperson]

Hi Guys,
I'm having the same problem. I have a digital PH meter and just buffered my PH from 8.1 to 8.39 as a test. I used Seachem Reef 8.3 buffer. I just watched it slowly drop from 8.39 to 8.29 in about 90 minutes. Not sure if it has stablized yet. I dose with Kalk. every night about 2tsp mixed in a 1/2gal. I do not slow drip it, It's goes in slow takes about half hour. not a slurry like Calfo though. I know I have quite a bit of kalk fall out in this amount of water, but I don't evaporate any more then 1/2gal. My tank is right next to a double window which I keep open. I'm not sure what could be causing the low PH?

Tom

[Randy Holmes-Farley]

Inside the house the pH only went up like 0.02 or something like that. Outside the house the pH went up by over .20 units(from 8.1x to 8.3x).

OK, then the choices are more fresh room air, or more limewater.

I'm having the same problem. I have a digital PH meter and just buffered my PH from 8.1 to 8.39 as a test. I used Seachem Reef 8.3 buffer.

Buffers are almost never a good way to raise pH. They will push alkalinity too high and often do not keep the pH adequately high.

I dose with Kalk. every night about 2tsp mixed in a 1/2gal. I do not slow drip it, It's goes in slow takes about half hour. not a slurry like Calfo though.

Sounds like too much too fast to me. Have you ever measured to see how high the tank pH gets by the end of that addition? I think it may be too high.

[Casperson]

Hi Randy, I have measured before and it stay's within a .2 range. My problem is, it doesn't stay there. By morning it's back down to 8.0 and will only rise to 8.14 during full photoperiod. My tank is next to a window thats open all day now. Today I'm adding an air stone in the sump to see if that will help. Is it important that my skimmer get outside air? The venturi hose is in the sump which is in the cabinet. I have been keeping the doors open but really don't want to. Any other suggestions?

Thanks,

[Randy Holmes-Farley]

Any other suggestions?

Try the aeration experiment in the article above to see if you need more aeration, or fresher air.

[Casperson]

Hi Randy,
Did the aeration experiment. My PH went up .1 after 1 hr. aeration for inside and the same for outside air. So it looks like I might need more aeration. At least I know my inside air is ok.
Any thoughts on what would be the best way to get more oxygen in the tank?

Thanks

[Randy Holmes-Farley]

A skimmer is usually a good way. An airstone in a sump that is otherwise closed can also help. Opening the top or ventilating a closed tank can help.
Bear in mind that it isn't adding more O2, it is taking out CO2. They are not necessarily inversely related. :)

[Casperson]

Thanks Randy, I'll give them a try. I have a skimmer, but what I can do is attach an air hose that takes air in from outside the cabinet. And I can add an air stone in the sump. How long before I would see a difference?

Tom

[Randy Holmes-Farley]

If such changes will make a detectable difference, you'd see it in 24 h or so.

[Casperson]

Hey Randy,

"Did the aeration experiment. My PH went up .1 after 1 hr. aeration for inside and the same for outside air."

My average tank PH is ranging from 7.8 (evening) - 8.0(daytime). If I use the above experiment as a guide, would I be correct in saying my PH will only rise .1? OR is the experiment not reaching air equilibrium in 1hr.?

Thanks,
Tom

[Randy Holmes-Farley]

With enough aeration with normal air, the pH will rise to 8.2 or even higher. But some people actually see a drop or no change on aeration with inside air, indicating excess CO2 in the air. The outside test helps gauge what to expect to see inside if there is normal air inside.

[Casperson]

Thanks Randy, Trying to think of what kind of air pump and how much would make enough of a difference? I've opened my cabinet under my tank and just started running a fan over my sump. Also lifted my canopy up a few inches so air can circulate through. It's 4pm and PH is 7.92.
All this is a great experiment for the planning of my new tank.
I'm doing a 150 gallon in wall at our new home. :)

Tom

[Randy Holmes-Farley]

Airstones usually make only a small difference, unless used in an area that otherwise gets no aeration (like an enclosed sump). In that case, the more the merrier. :)

I'm doing a 150 gallon in wall at our new home.

:thumbsup:

Good luck with it. :)

[Casperson]

Randy, Just re-tested my outside air. Here's what happened. I got to thinking about how I tested my outside air yesterday? (air pump on an open window with the cup of water inside the window! duh! Tried again tonight, only this time went out to my deck with my airstone and cup of water and a corona with lime :) And aerated for about 2 hrs. A few coronas' later I tested PH. Went from 7.93 to 8.23! wouldn't you consider this a substancial jump. I'm in the middle of an inside air test again. No coronas. How can I get this outside air into my tank!

Tom C.
For Corona :P
Could lack of O2 in my house be why I'm tired all the time at home,
or could it just be my wife and kids?

[Casperson]

Just examined my indside test for PH 7.84. So thats a big difference from outside air.
Any ideas on how I can get to that air?

[Randy Holmes-Farley]

Yes that shows you have substantial elevated inside CO2. Open windows and air exchangers (expensive, but saves on heating costs) are good ways to bring in fresh air, but limewater (kalkwasser) will help even without the fresher air.

[LBCBJ]

I agree with increased aeration, poor circulation can lead to excessive CO2 in the water. Over time metabolic compounds and phosphates also tend to accumulate which can lower pH (often a problem in older tanks), so more frequent water changes may help also.

[Randy Holmes-Farley]

Water changes are not usually a suitable solution to pH problems, IMO. I'm not sure what you mean by metabolic compounds, but phosphate in the water would not tend to reduce the pH.

[LBCBJ]

I really should have said organic acids and phospahates, which can deplete the buffer capacity or alkalinty of the water. The acids can deplete calcium carbonate and bicarbonates from the water, and the phosphate, while mabey not a common problem, can lower alkalinity by precipitating out of soultion in compounds with calcium and magnesium, therefore lowering the pH of the water over time.

[Randy Holmes-Farley]

If there is a lot of organic matter in the water, some of it will be detected as alkalinity (carboxylic acids on the organic compounds will be partially titrated by ph 4.2, for example), so it can make the bicarbonate/carbonate alkalinity "appear" higher than it actually is.

In that case, lower pH is still driven by the carbonate/bicarbonate alkalinity and the CO2 level, but the true carbonate/bicarbonate alkalinity may be lower than the aquarist measured with a total alkalinity test kit.