Question about PH (+KH/CO2)

[Canuck]

Agreed the pH may only fall by 1 point but that is a dramatic enough change to kill a fish if it happens too fast.

Not when using CO2 to alter pH, I've swung the pH up by almost a full unit when doing a water change in 15 minutes. Fish didn't notice a thing. Try that with pH up and see what happens (at least if your not emotionally attached to your fish.) Granted going down takes longer but my pH may fall by a full unit in less then 8 hours, I wouldn't try that with a chemical. Absolutely no signs of stress from my fish.

The key to preventing CO2 from altering the pH is making sure the water is properly buffered (proper KH level).

CO2 alters pH, and similar amounts of CO2 alter pH by the same amount whether the kH is 1, 3, 5 or 10.

 

[H3D]

Not when using CO2 to alter pH, I've swung the pH up by almost a full unit when doing a water change in 15 minutes. Fish didn't notice a thing. Try that with pH up and see what happens (at least if your not emotionally attached to your fish.) Granted going down takes longer but my pH may fall by a full unit in less then 8 hours, I wouldn't try that with a chemical. Absolutely no signs of stress from my fish.

I never said all fish. Results may vary. However a pH swing of even 1 point can kill some fish.

CO2 alters pH, and similar amounts of CO2 alter pH by the same amount whether the kH is 1, 3, 5 or 10.

When you are talking about adding CO2 to just tap water, then yes. But the carbonic acid produced by CO2 is not the only form of acid in aquarium water. So this information is only good for talking about "water" and C02 only, not an actual aquarium.

I would also like to point out that adding C02 continuously lowers the KH. So if you start with a low KH and don't replenish the buffer, the acids will eventually over eat up the buffer and cause a HUGE pH swing. That is why it is vital to monitor the KH.

 

[H3D]

CO2 does not effect water hardness, TDS, KH, etc.

CO2 does effect KH. The carbonic acid formed by adding CO2 (along with the other acids present in aquarium water) will slowly eat through the carbonate buffer (KH) until it reaches zero. Doing water changes or adding baking soda replenishes the buffer.

 

[loaches r cool]

I meant by going from no added co2 to 30ppm does not change anything enough to effect fish (osmotic shock) despite a rapid full point pH change. Over a long period of time it could I suppose, and since you mentioned it please tell me at what rate 30ppm of co2 will 'eat' KH (excluding other acids in the tank), I'd like to know. I've gone two weeks between water changes somewhat frequently (often gone on my days off and work long hours on working days, etc.) and did not see any discernible change in KH. Of course evaporation and a few other things my help to hide that.

 

[Canuck]

Carbonic acid formed when CO2 is injected is a very weak acid, it will affect kH but the acids produced from fish waste will destroy your buffer long before CO2 will have any appreciable effect at 30 ppm.

Obviously H3D has kept different fish then I have. You couldn't tell me which fish are that sensitive to pH swings caused by CO2 injection? And have you seen it first hand? I'm not trying to be argumentative but I've been reading plant forums for a long time and 99% of the problems attributed to pH swings seem to have some other underlying cause.

 

[H3D]

I meant by going from no added co2 to 30ppm does not change anything enough to effect fish (osmotic shock) despite a rapid full point pH change. Over a long period of time it could I suppose, and since you mentioned it please tell me at what rate 30ppm of co2 will 'eat' KH (excluding other acids in the tank), I'd like to know. I've gone two weeks between water changes somewhat frequently (often gone on my days off and work long hours on working days, etc.) and did not see any discernible change in KH. Of course evaporation and a few other things my help to hide that.

In the scenario you give the there are too many variables to give you a prediction. I don't know how much buffer is in your tank. Nor do I know how much carbonic acid you are adding to the tank. The buffer will hold as long as there is not more carbonic acid than carbonate buffer. Again this does not account for the other acids in your tank.

My point was that a tank with a low KH is always on the edge of a giant pH swing if the buffer gets used up, not just one point like you are suggesting. Adding CO2 can cause the buffer to be used up faster. That is why it is important to monitor the KH. If you don't want to monitor your KH no one is forcing you too.

Carbonic acid formed when CO2 is injected is a very weak acid, it will affect kH but the acids produced from fish waste will destroy your buffer long before CO2 will have any appreciable effect at 30 ppm.

Agreed. That was my point. Just talking about CO2 and water is meaningless because the other acids formed need to be taken in to account.

I've been reading plant forums for a long time and 99% of the problems attributed to pH swings seem to have some other underlying cause.

The problem with that is the other "underlying causes" could be a result of the pH change. For instance low amounts of 02 in the water or that NH3 becomes more toxic to fish as the pH level is decreased.

 

[Star_Rider]

I'll just add that pH is used to help measure the CO2 injected into t a tank. you do need to know the kh as a starting point. and it is important as too much CO2 and the fish may starve for O2.

 

[loaches r cool]

The problem with that is the other "underlying causes" could be a result of the pH change. For instance low amounts of 02 in the water or that NH3 becomes more toxic to fish as the pH level is decreased.

Actually you got that backwards, ammonia becomes more toxic as pH rises. Another good reason not to unnecessarily increase KH.

Agreed. That was my point. Just talking about CO2 and water is meaningless because the other acids formed need to be taken in to account.

It is not completely meaningless and you should be able to calculate it. Taking just co2 and KH into account you can ignore the other factors that make this impossible to determine, you have a fixed water volume and fixed co2 and KH amounts. I didnt mention the reason I was curious, but its about a drop checker. If co2 really 'ate up' KH at any appreciable rate then a drop checker which relies on a precise KH value, would become wrong quickly. The only acids and bases in it should be CO2 and baking soda. But many claim they work well over a month, personally I redo mine in about a months time, I might have to do a test to determine how long they will continue to operate accurately.

 

[H3D]

Actually you got that backwards, ammonia becomes more toxic as pH rises. Another good reason not to unnecessarily increase KH.

No I don't. As pH increases, the ammonia "levels" in the water increase. However the toxicity of the ammonia is found to be greater at lower levels in a lower pH.

It is not completely meaningless and you should be able to calculate it. Taking just co2 and KH into account you can ignore the other factors that make this impossible to determine, you have a fixed water volume and fixed co2 and KH amounts. I didnt mention the reason I was curious, but its about a drop checker. If co2 really 'ate up' KH at any appreciable rate then a drop checker which relies on a precise KH value, would become wrong quickly. The only acids and bases in it should be CO2 and baking soda. But many claim they work well over a month, personally I redo mine in about a months time, I might have to do a test to determine how long they will continue to operate accurately.

You can calculate it, however it is not a simple thing to do. You would need to know the amounts of each component of the buffer that are in the water as well as the amount of carbonic acid and the rate at which it is being added to the water.

It is possible that the buffer could hold for a lot longer than a month depending on its capacity. Again Carbonic acid is a week acid so it has a small effect on the buffer. The reason a low KH in an aquarium is potentially more dangerous is because there are other acids in the water.

 

[loaches r cool]

No I don't. As pH increases, the ammonia "levels" in the water increase. However the toxicity of the ammonia is found to be greater at lower levels in a lower pH.

Technically I suppose this is correct, but unless it is another myth that needs busting, higher pH levels are far more hazardous. The rise in NH3 levels with a rise in pH is far greater than the rise in toxicity with lower pH, at least thats the common thought, I havent run the numbers.