Originally Posted by chagovatoloco
"Fish keeping does not add CO2 to control pH though.
They use buffers like baking soda.
When the pH drops fast, it's a sign of some cycling going very wrong in a fish only tank, when you add say 4 Kh more baking soda to a 2 Kh tank, the fish will die and the pH will shoot up fast.
CO2 is not the same.
Think about this thought question:
What happens if I do a massive 60-70% weekly water change when I add CO2 and have a pH of 6.2, and the incoming tap is 7.6?
How much pH change do I see over a few minutes?
About 1 full unit.
The KH is the same with respect to the tap water and the tank water.
So the osmotic difference is the same, CO2 is not a salt.
Now, think about what folks do using CO2 and in planted tanks with 50% weekly water changes......
Any reports of dead fish?
Healthy happy fish and plants?
I'll let you ponder the rest and see how pH, at least in and of itself is not really the issue, rather the KH/buffering systems that change rapidly, and thereby also by definition, change the pH, are the real issue with respect to fish health.
Fish hobbyist hardly know beans about GH, KH, and chemistry of the pH/KH/CO2 system as it is. And then only in relation to ambient, not fertilization with CO2 ppms.
So that causes myths and confusion."
Partially deleted to save band width.
Let me point something out. I consider myself at the intermediate level when it comes to growing plants in an aquarium but I am a professional (which means that I get paid to do this) expert at chemistry and my special interest right now is water chemistry.
So I probably know more than Tom Barr and Takashi Amano combined about that subject.
So if Tom Barr says:
“Fish keeping does not add CO2 to control pH though.
They use buffers like baking soda.”
He obviously doesn’t know anything about water chemistry.
I don’t know how to put a full semester of P. Chem. into a short post but let see if I can explain something.
CO2 = H2CO3= HCO3- = CO3(-2)
What this means is that any of these species will convert to the other and all are present in water. The amount of each depends on the pH and the amount of spectator ions like Na (referred to in aquarium literature as kH).
So when you add baking soda (NaHCO3) to your tank you are adding CO2 as well. In fact, one of the ways they make baking soda is by adding CO2 to a solution of Na2CO3.
Plants can crack out most of this CO2 and do so until the pH reaches about 8.4, which is the equilibrium point for the HCO3- = CO3(-2) reaction.
So when you add CO2 you are simply adjusting the relative levels of H2CO3, HCO3- and CO3(-2).
When Barr says:
“When the pH drops fast, it's a sign of some cycling going very wrong in a fish only tank, when you add say 4 Kh more baking soda to a 2 Kh tank, the fish will die and the pH will shoot up fast.”
(Let me point out that he is a little confused about whether the pH goes up or down but that is not my point).
My point is that when you add 4kH more baking soda, the pH will go to 8.4 and you will increase the CO2 by 70 ppm (This CO2 is not usable by plants; since, they cannot crack it out at that pH). You could get every mg of this CO2 out simply by adjusting the pH down.
Now this is my experience after keeping fish over 30 years.
In a low kH/gH tank changes in pH are not necessarily fatal; however, lower pH is beneficial/necessary for many species. If you want to keep and breed these you will have to maintain a low pH.
BTW: There is no place in the Barr quote where he says he actually used one only the same type of off the top of your head stuff that everyone else is using on this thread. So far, no one has actually used one; so, they are all hypothecating.