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View Full Version : Fish only tank consumes 2.7 dkh of ALK per day


xenon
04/05/2012, 08:48 PM
I am really puzzled by the amount of alkalinity my 6g nano tank consumes.

I dose 9.6ml of BRS Recipe 1 every 24hrs to maintain 9dkh. That means it drops to 6.3 dkh every 24hrs.

The only thing in there is a small 4" RBTA, 1 true perc, 1 firefish, 1 shrimp and a cleanup crew.

Any ideas?

I use a Hanna Meter to test Alk. I have been through a few reagents so its not a faulty test. I actually test every 24hrs because I am so paranoid.

ek9vboi
04/05/2012, 09:00 PM
Depending on how old the set up is, it could be that coralline algae is consuming it. It's sort of irrelevant but how often are you doing water changes for such a small tank? Any issues with the larger tank?

FragIt Dan
04/05/2012, 09:16 PM
Clearly there is something fishy going on. Where the issue lies is hard to determine from the info you have given. Are you testing before and after dosing to verify you are in fact raising the dkh that much with your dose? Assuming your tank is actually consuming carbonates at that rate (not a safe assumption for me given the info), the only things I know of that will bring your dkh down are liquid phosphate destroyers and excessively high calcium, the later of which will be evident from calcareous deposits on your pumps. For now, I would test dkh, add your dose, and retest dkh about 30min later to verify your dosing is having the effect you think it does.

xenon
04/05/2012, 09:40 PM
Clearly there is something fishy going on. Where the issue lies is hard to determine from the info you have given. Are you testing before and after dosing to verify you are in fact raising the dkh that much with your dose? Assuming your tank is actually consuming carbonates at that rate (not a safe assumption for me given the info), the only things I know of that will bring your dkh down are liquid phosphate destroyers and excessively high calcium, the later of which will be evident from calcareous deposits on your pumps. For now, I would test dkh, add your dose, and retest dkh about 30min later to verify your dosing is having the effect you think it does.

Yes I do test before/after. Here are the results of my test today.

10:30 pm
alk: 112 ppm = 6.3 dkh
dose: 9.6 ml to 9 dkh

11:30 pm
alk: 157 ppm = 8.8 dkh

xenon
04/05/2012, 09:42 PM
Depending on how old the set up is, it could be that coralline algae is consuming it. It's sort of irrelevant but how often are you doing water changes for such a small tank? Any issues with the larger tank?

The tank is fairly new. (4 months old)

I would be shocked if coraline was consuming that amount. Besides, I don't see much if any coraline growth anyways.

I do a 50% water change per week. (i love to overfeed) :)

xenon
04/05/2012, 09:43 PM
To make things more interesting.

I do not consume any calcium what so ever.

bertoni
04/05/2012, 09:45 PM
If the tank has coralline, that could explain all the consumption, IME. My soft coral tanks regularly consumed that much per day.

xenon
04/05/2012, 09:51 PM
If the tank has coralline, that could explain all the consumption, IME. My soft coral tanks regularly consumed that much per day.

The tank may have some green coraline but not much purple.

How in the world do your corals thrive with an Alk swing like that everyday?

bertoni
04/05/2012, 09:54 PM
Soft corals don't care about the alkalinity. :) Neither do fish. :) They both grew faster than was necessary.

I suspect you're seeing coralline growth. I might check inside the larger pumps or the surface of the heater, the area around the dosing point, etc, for signs of precipitation, though.

xenon
04/05/2012, 10:01 PM
Soft corals don't care about the alkalinity. :) Neither do fish. :) They both grew faster than was necessary.

I suspect you're seeing coralline growth. I might check inside the larger pumps or the surface of the heater, the area around the dosing point, etc, for signs of precipitation, though.

I cleaned out the wet side of my Vortech MP10 today, nothing.

Room temp is always 79-80 so I don't use a heater.

I am pretty sure fish do care about alkalinity because low alk = low PH.

Masterofnonsense
04/05/2012, 10:53 PM
In addition to precipitation on the inside of your pumps and your heater, your sand might clump up as well.

You could try switching to Recipe 2 to see if your numbers stay more in line.

xenon
04/05/2012, 11:36 PM
In addition to precipitation on the inside of your pumps and your heater, your sand might clump up as well.

You could try switching to Recipe 2 to see if your numbers stay more in line.

Interesting. I think you are on to something here.

My sand has been clumping up. I got 10 small nassarius snails to stir it up but so far these snails are totally useless. lol

So what is causing the sand to consume all this alk?

Masterofnonsense
04/06/2012, 12:29 AM
Interesting. I think you are on to something here.

My sand has been clumping up. I got 10 small nassarius snails to stir it up but so far these snails are totally useless. lol

So what is causing the sand to consume all this alk?

I believe it precipitation of the alk into the sand which then hardens up and creates the clumps. When you dose Recipe 1 it raises your pH and makes precipitation much more likely. If you don't have any trouble keeping your pH over 8 I'd switch to Recipe 2. It doesn't raise your pH at all, and is less prone to causing precipitation.

I had the same problem you are having, and switched to Recipe 2 and things have been much better.

tmz
04/06/2012, 12:35 AM
low alk = low PH.
Not exactly , high CO2 = low ph. High ph and low alk is possible and vice versa.

I do not consume any calcium what so ever
So what is causing the sand to consume all this alk
Calcium depletes only 20ppm for each meq/l of alk(2.8dkh) as caclium carbonate forms( it is 50ppm carbonate and 20ppm calcium approximately) , so calcium depletion it is often within the range of testing noiseeven when alk depletions are more obvious.
Precipitation of calcium carbonate may occur in sand beds as localized acidic conditions from bacterial activity lead to some sand dissolving with a consequent jump in ph from the extra dissolved calcium and carbonate, followed by precipitation. As new calcium carbonate crystals form and clump the sand they likely,imo, take more alk out of the water than dissolving sand puts in as evidenced by the extra material filling voids when the sand clumps.Soft leather corals use some calcium carbonate to form sclerites ,bone like shards inside which help them stand up but an anemone shouldn't care about alk. Stony corals also use a good deal.
Coraline uses a lot.
What is your magnesium and sg and ph btw. ? Adeqaute magnesium discourages precipitation and helps limit some sand clumping ,ime.
I don't have experience with the alk checker so I can't comment on it's accuracy. I'd crosscheck it with another test.

FragIt Dan
04/06/2012, 01:08 AM
Awsome write up tmz and great comments from masterofnonsense and others... you guys never cease to amaze me.

Randy Holmes-Farley
04/06/2012, 07:15 AM
Alkalinity is depleted by the process of converting ammonia into nitrate. So when nitrate is accumulating, alkalinity will be depleted.

I address that here:


When Do Calcium and Alkalinity Demand Not Exactly Balance?
http://reefkeeping.com/issues/2004-12/rhf/index.htm


from it:

Alkalinity Decline in the Nitrogen Cycle

One of the best known chemical cycles in aquaria is the nitrogen cycle. In it, ammonia excreted by fish and other organisms is converted into nitrate. This conversion produces acid, H+ (or uses alkalinity depending on how one chooses to look at it), as shown in equation 1:

(1) NH3 + 2O2 --> NO3- + H+ + H2O
For each ammonia molecule converted into nitrate, one hydrogen ion (H+) is produced. If nitrate is allowed to accumulate to 50 ppm, the addition of this acid will deplete 0.8 meq/L (2.3 dKH) of alkalinity.

However, the news is not all bad. When this nitrate proceeds further along the nitrogen cycle, depleted alkalinity is returned in exactly the amount lost. For example, if the nitrate is allowed to be converted into N2 in a sand bed, one of the products is bicarbonate, as shown in equation 2 (below) for the breakdown of glucose and nitrate under typical anoxic conditions as might happen in a deep sand bed:

(2) 4NO3- + 5/6 C6H12O6 (glucose) + 4H2O --> 2 N2 + 7H2O + 4HCO3- + CO2

In equation 2 we see that exactly one bicarbonate ion is produced for each nitrate ion consumed. Consequently, the alkalinity gain is 0.8 meq/L (2.3 dKH) for every 50 ppm of nitrate consumed.

Likewise, equation 3 (below) shows the uptake of nitrate and CO2 into macroalgae to form typical organic molecules:

(3) 122 CO2 + 122 H2O + 16 NO3- --> C106H260O106N16 + 138 O2 + 16 HCO3-

Again, one bicarbonate ion is produced for each nitrate ion consumed.

It turns out that as long as the nitrate concentration is stable, regardless of its actual value, there is no ongoing net depletion of alkalinity. Of course, alkalinity was depleted to reach that value, but once it stabilizes, there is no continuing alkalinity depletion because the export processes described above are exactly balancing the depletion from nitrification (the conversion of ammonia to nitrate).

There are, however, circumstances where the alkalinity is lost in the conversion of ammonia to nitrate, and is never returned. The most likely scenario to be important in reef aquaria is when nitrate is removed through water changes. In that case, each water change takes out some nitrate, and if the system produces nitrate to get back to some stable level, the alkalinity again becomes depleted.


Figure 4. Porites species vary with respect to the amount of magnesium incorporated, from less than 0.1% to over 1% magnesium in the skeleton. Photo courtesy of Skip Attix.
If, for example, nitrate averages 50 ppm at each water change, then over the course of a year with 10 water changes of 20% each, the alkalinity will be depleted by 1.6 meq/L (4.5 dKH) over the course of that entire time period. This process is one of the primary reasons that fish-only aquaria that often export nitrate in water changes need occasional buffer additions to replace that depleted alkalinity.

While the magnitude of the depletion described in the paragraph above is fairly easy to understand, it also can be converted into units that clarify the imbalance. The impact of alkalinity depletion on the calcium and alkalinity demand balance depends, of course, on the amount of calcium and alkalinity added (and consumed) over the course of that same year.

For a typical reef aquarium (assuming a daily addition of saturated limewater equal to 2% of the tank's volume), the amount of alkalinity added during the course of a year is 297.8 meq/L. Likewise, the amount of calcium added is 5,957 ppm Ca++, given the ratio of 1 meq/L of alkalinity for every 20 ppm of calcium that has been discussed above. If that 1.6 meq/L of alkalinity is added to create a larger demand of 299.4 meq/L over the course of a year, the new ratio for the total demand becomes 19.90 ppm Ca++ per 1 meq/L of alkalinity. Consequently, while this effect of nitrate production on alkalinity is enough to be noticed over the course of a year, it is substantially smaller than the other effects discussed in this article, and is unimportant for aquaria that maintain low nitrate levels.

xenon
04/06/2012, 09:58 AM
BINGO!

Alkalinity is depleted by the process of converting ammonia into nitrate.

I love to overfeed in this tank so I do 50% water changes per week to maintain reasonable nitrate levels.

So the nitrogen cycle is what is causing my alk to deplete. I would have never guessed.

How to I prevent this from happening?

Randy Holmes-Farley
04/06/2012, 10:49 AM
If the drop is from nitrification, then you can just add back the alkalinity lost, as you have been, or you can use a different method for reducing nitrate. Most of those other methods add back the lost alkalinity (except sulfur denitrators).

xenon
04/06/2012, 11:32 AM
If the drop is from nitrification, then you can just add back the alkalinity lost, as you have been, or you can use a different method for reducing nitrate. Most of those other methods add back the lost alkalinity (except sulfur denitrators).

I don't mind adding the Alk back daily but the clumping sand is becoming an issue.

Would you agree that dosing sodium bicarbonate instead of soda ash will eliminate that issue?

Randy Holmes-Farley
04/06/2012, 12:01 PM
Well, the clumping sand is probably the main sink. I must have missed mention of that.

Why not let the alk drop to 6-7 dKH? That's natural for the ocean and the things you have should do fine. :)

xenon
04/06/2012, 12:14 PM
Well, the clumping sand is probably the main sink. I must have missed mention of that.

Why not let the alk drop to 6-7 dKH? That's natural for the ocean and the things you have should do fine. :)

I am letting it drop to 6.3 but the alk swing is what is bugging me.

I was planning to add some corals but there is no way I can until I get the alk more stable.

If I siphon the clumps of sand, will that solve my problem?

Randy Holmes-Farley
04/06/2012, 12:19 PM
It won't drop nearly as fast if you just try to keep it in the 6-7 dKH range. The drop goes faster and faster as alk and pH rise.

No, siphoning usually is not useful.

How old is the tank? It usually goes away on its own after a while.

xenon
04/06/2012, 12:36 PM
It won't drop nearly as fast if you just try to keep it in the 6-7 dKH range. The drop goes faster and faster as alk and pH rise.

No, siphoning usually is not useful.

How old is the tank? It usually goes away on its own after a while.

It would need to dose all day long to keep it stable.

The design of the tank makes it impossible to run any type of equipment to maintain solid parameters so that is why I decided large frequent water changes would be ideal for such a small body of water.

http://dl.dropbox.com/u/26003034/fluval-edge/19.JPG

Randy Holmes-Farley
04/06/2012, 12:47 PM
I think you won't need to dose much at all to keep it stable at 6-7 dKH. Alk rarely drops below 6 dKH in any reef tank, even with no dosing.

bertoni
04/06/2012, 02:51 PM
If the nitrification process is consuming the alkalinity, I'd expect the calcium to rise substantially over the long haul, compared to alkalinity. I guess I don't know whether you're dosing the calcium part. 50% water changes are very large, for that matter.

I agree that clumping sand can consume a lot of alkalinity and calcium.

xenon
04/06/2012, 03:37 PM
I think you won't need to dose much at all to keep it stable at 6-7 dKH. Alk rarely drops below 6 dKH in any reef tank, even with no dosing.

Well, I can say that my alk will drop well bellow 6 dkh because just last week I was at 4.5 dkh and that is when I started noticing how much alk I was consuming.

tmz
04/06/2012, 03:53 PM
Randy , Thanks for pointing out the ammonia /nitrate /carbonate alk relationships. I've read the article you cited many times and still go back to reference it. Very helpful.

Ime, clumping seems to happen more often when sand is new to a tank and at higher alk levels particularly with low magnesium.
It does ,as you noted, slow down/ stop after a while without other changes.
Regarding the duration of the clumping ,maybe, organics in the sand: degrade , feed the nitrification and denitrification cylce and sink the carbonate from NO3 to N2 conversion as calcium carbonate thus welding the sand together. The process may slow down or stop when the organics in/on the sand are exhausted.
I guess some(C,N and P) from the water would diffuse into the sand too but maybe not enough to cause significant clumping. If the diffusion is substantial and ongoing , the culmping would likely just keep going, I think.
Do you think , some aragonite could dissolve along the way in hypoxic conditions generated by denitrifying bacteria as well and consequent precipitation could sink some extra carbonate beyond that contributed by any dissolution or anaerobic denitrification.?

Randy Holmes-Farley
04/06/2012, 05:24 PM
Well, I can say that my alk will drop well bellow 6 dkh because just last week I was at 4.5 dkh and that is when I started noticing how much alk I was consuming.

Well, it will depend on pH and other factors (like magnesium), but as alk drops below 6 dKH the consumption becomes quite slow. In any case, you will need far less supplement to maintain 6-7 dKH than 9 dKH. :)

Waht salt mix are you using? It may be low in magnesium.