Help With Co2 Injection Lowering Ph

[confusion]

I have a 30G planted tank that I recently started adding CO2 to. I'm using one of the fizzy tab deals with the upside down box to hold an air bubble.

My problem is that I've had 2 gouramis die on me in the past month. At first, I thought that the gouramis were gulping CO2 out of the box, but I just checked my PH and it's very low - around 6.

My normal ph is between 6.8 and 6.4, so the co2 is obviously having an effect, which as I understand it means that my buffering ability is low. What can I do to keep the ph stable in a tank with CO2 being added?

PS I tried to search the forum, but there is a limit on how short the search terms can be - "low ph" is too short, even with the quotes.

 

[paulf]

A ph of 6 is very low, do you know the kh?
Sounds like you have too much c02 in there??? download a c02 calculator, theres a few out there and check what it is
I get concerned when my ph goes down to what your tapwater is, with c02 I would add an airstone to put the oxygen back in the water and not use c02 until you have checked the stats

 

[Themuleous]

A pH of 6 is fine, lots of people run planted tanks at the pH and lower. As said above, whats your KH and PH? Those bell type diffusers are not very good BTW, so I doubt you're getting much CO2 into the tank anyway.

Sam

 

[paulf]

A pH of 6 is fine, lots of people run planted tanks at the pH and lower.

I dont know anyone that runs a tank with a ph of 6 and I certainly wouldn't want to inject c02 into that water

 

[Themuleous]

99% of people who use ADA aquasoil run a tank with a pH of around 6 (possibly less) due to the fact that it removes the KH from the water. I wont list them all. They all also run CO2, often at rate well over 30ppm (I've seen tanks at 100ppm with a bubble rate of 1 or 2 bubbles per second in 60lt tanks)

Sam

 

[confusion]

I don't yet have a kh test kit - one is on order. The ph of my tap water is about 6.4. I have a CO2 indicator that uses the liquid in a small bell to display color. I can tell that the CO2 does dissolve pretty effectively, as it dissapears from the bell within about 2 hours and the co2 indicator changes from "low" to "good". I was only able to get it to "good" by continuing to feed co2 into the bell as it was dissolved.

I haven't done much research on this yet, but is there a way to adjust kh to better control ph swings, or is it a matter of more accurately controlling the amount of co2 I put into the water?

 

[Themuleous]

As a brief bit of background to Co2, CO2/KH/pH are all lock in a fixed relationship. This relationship allows us to work out the CO2 of a tank, i.e if you know the ph and Kh of the tank you can work out the CO2. It is always the pH that changes in the tank, change either the KH or CO2 the pH changes. i.e. increase CO2 or decrease KH the pH goes down, decrease CO2 or increase KH and the pH goes up. Its fixed.

But in answer to your question, I would leave the kh well a lone, chances are you do have some in your tap water and tank, in which case providing you do regular water changes you shouldn't have a problem. Constantly adding bicarb is going to be a hassle.

Sam

 

[themissingelf]

Do you leave the CO2 running when the tank lights are off? If you do, when do you measure your PH? C02 is consumed by plants when the lights are on and produced by plants when the lights go off. If you're adding CO2 during "lights off", you need test PH just before the tank lights come on and again just before they go off in order to check the swing of PH.

Although fermentation kits rarely produce a lot of CO2, if your KH is low, then it could be that the CO2 (if left running overnight) is building up enough to drop your PH even lower than you think.

If KH is low (less than 4), then it increases the chances of large swings in PH which are more likely to kill your fish than simply a low PH.

 

[CBBP]

99% of people who use ADA aquasoil run a tank with a pH of around 6 (possibly less) due to the fact that it removes the KH from the water. I wont list them all. They all also run CO2, often at rate well over 30ppm (I've seen tanks at 100ppm with a bubble rate of 1 or 2 bubbles per second in 60lt tanks)

Sam

I certainly do.. well.. actually I found a way to keep it at 5.8-6.2 haha.. just find some tipe of rock that increases PH and put a small ammount in your filter.. that is what i did when i got ADA AS. Keeps it nice and stable. but a PH of 5.8 did not kill my fish..

 

[Puffer punk]

put some coral sand/gravel in ur filter but only a little bit and it shud help stableize ur ph

 

[Themuleous]

If KH is low (less than 4), then it increases the chances of large swings in PH which are more likely to kill your fish than simply a low PH.

Thats not strictly true, the relationship between kh/ph/co2 is fixed, a low kh is no more unstable than a high kh, you just have to carry out regular water changes to keep the KH maintained, thats all. the only way you're going to get a large ph swing if is literally 100% of the KH gets removed, then the water has NO buffering so the pH is free to swing wherever it wants. Even a KH of 0.5 would give you a stable pH.

I got this from Chuck

Myth: A Low KH results in a larger pH swing when adding CO2.

Many people are under the mistaken impression that a low KH results in large pH swings when adding CO2, while raising the KH will result in smaller pH swings. This is not the case. The KH will move the start and end pH values, but the pH swing will be the same for a given level of CO2. You can see this in the chart below, or using the calculation:

Case 1: Assume a KH of 15 degrees, and a starting CO2 level of 4.5ppm, which would result in a pH of 8.0. If we then add CO2, to increase the CO2 level to 28ppm, that would drop the pH down to 7.2, for a pH shift of .8.

Case 2: Assume a KH of just 1.5 degrees, and a starting CO2 level of 4.5ppm, which would result in a pH of 7.0. If we then add CO2, to increase the CO2 level to 28ppm, that would drop the pH down to 6.2, for a pH shift of .8, the exact same as in case 1.

One possible explanation for this myth is that many copies of this pH chart skip some of the higher pH values, for example, jumping from pH 7.4 to a pH of 8.0. If the reader didn't pay careful attention, they might mis-interpret the size of the pH swing. I specifically made sure to include all pH values, between 6 and 8, in steps of .2.

This relationship will break down at extremely low KH levels (below 1 degree), when there isn't enough carbonate to completely buffer the acids present. In that case, the pH can drop quickly and dramatically. But if the KH is 1 degree or higher, then the size of the pH swing when injecting CO2 will be determined only by the amount of CO2 dissolved in the water.

I run both my CO2 kits 24/7, I find its best to test at lights off, if the pH/KH gives you a CO2 of 30ppm at lights off then you know that there will be at least that much at lights on.

Sam

 

[Waterloo Kid]

I was under the impression that the buffering capacity of the Kh is finite. By that I mean that an given KH value has the ability to buffer only so much acidic compound. Once this buffer is used up you will see the sudden 'snap' changes in pH that cause so many problems. I understand that passage from Chuck but isn't that refering to the pH swing that is intentionally caused whilst increasing the CO2 level by any particular level. The problem with low KH is, as I found out, that the compounds that contribute to the KH value are slowly used up by an aquarium. So whaere as one day you might have injected, say, 3 bubbles per second for 24 hours and everything was fine, the next day (after the KH compounds have reduced by a small amount) that same 3 bubbles per second pushes the CO2 concentration just a bit too far. the CO2 produces too high a level of acidic compounds (carbonic acid if I remember correctly) and the KH is overwhelmed. Then you suddenly get your dreaded pH crash. Theoretically a very small KH wil keep your tank stable so long as the Kh remains constant.
I use a piece of limestone in my tank filter to keep my KH at about 4 degrees. The beauty of this is that the lower the pH the more limestone dissolves to help bolster the KH (limestone dissolves in acidic mediums producing carbonate ions). I haven't had any more problems with the pH of my tank since adding the rock.

That's my (not very scientific) understanding of it anyway.

WK

 

[Themuleous]

TBH mate, I dont really understand how it works, all I know is that I run CO2 24/7 and I've never had a problem, I also know that people have undetectable levels of KH (when using ADA AS) and they pump CO2 into their tanks at a huge rate, but to very large and regular water changes.

Sam

 

[Waterloo Kid]

I'd guess that in those cases there's something else in the water buffering the pH other than carbonate ions. You can't fill an unbuffered tank with carbonic acid without the pH dropping through the floor. I wonder what it is?

WK