Why Alkalinity Rises in Pools using CO2 for pH Management

If you don't feed CO2 on a pool, and you never have, that may not make a lot of sense to you because, you know, you're used to suppressing pH with manual additions of acid, or maybe you have an acid feeder.

And that's fine.

That does the job too.

But the way that acid lowers pH, as we've discussed, I think two episodes ago, acid neutralizes against alkalinity.

Specifically, it neutralizes against bicarbonate alkalinity, and that bicarbonate alkalinity converts into carbonic acid, which then dissociates into dissolved CO2 and water.

And when you have more CO2 in the water, that brings the pH down.

Then, as turbulence happens and time, you know, time and turbulence, you off-gas some of that CO2 because, quote-unquote, "The beer has to go flat again." Henry's Law kicks in.

So you lose that CO2 that was just created by the acid sort of burning through alkalinity.

That CO2 off-gases and your pH rises again.

So for pretty much every residential pool operator listening to this, that's what you're used to.

So you actually probably have never seen this phenomenon.

But if you're a commercial operator, or perhaps you have a very high-end customer that has CO2 on their backyard pool, which is rare, you have probably noticed that the alkalinity rises without you adding bicarb.

It just seems to naturally rise.

Now, the theory here has always been, well, the CO2 is raising the alkalinity.

N-no, not exactly.

Uh, and I'm going to explain exactly what's happening here, and I appreciate all the questions for encouraging me to look deeper into this.