Innate pH Buffering?

[arking_mark]

Very curious. Hope someone has some insight.

I recently had to treat a fish for intestinal worms. I decided on a 2-dose regimen of PraziPro and 2 weeks of Metroplex laced food. This meant 72 hrs no Skimmer / GAC, 48 hrs yes Skimmer / GAC, then another 72 hrs no skimmer /GAC.

1st 72 hrs of no skimmer / GAC and pH slowly came down.

48 hrs of back to normal brought my pH back to 8.35ish.

36 hrs into 2nd no skimmer / GAC pH has plummeted and I had to turn off Kalk dosing because Alk has climbed over 9.6dKH.

Red arrow indicates where the skimmer was turned off and green when it was turned back on. Skimmer has a recirculating CO2 scrubber (which is its primary function in my tank)
\

My question is why did the pH drop nice and slowly the 1st time and so quickly the 2nd time?

 

[Randy Holmes-Farley]

The pH buffering (that is, the real use of the term as it applies to reducing the changes in pH as a function of an acid or base added) depends both on the alkalinity (higher alk means more bufferign and less swing) and on the actual pH (lower pH in a reef tank gives more pH movement with added acid or base).

I discuss those here:

https://reefs.com/magazine/chemistry-and-the-aquarium-boron-in-a-reef-tank/

In this case, neither of these seems the likely explanation, and perhaps it is just that the CO2 level in the air was higher for some reason the second time, adding more acid (CO2) per minute the skimmer ran. Closed windows? More people around? More cooking with a gas appliance? less obvious situations that impact indoor CO2 are indoor air temp closer to outdoor (less convection)? less windy?

 

[arking_mark]

The pH buffering (that is, the real use of the term as it applies to reducing the changes in pH as a function of an acid or base added) depends both on the alkalinity (higher alk means more bufferign and less swing) and on the actual pH (lower pH in a reef tank gives more pH movement with added acid or base).

I discuss those here:

https://reefs.com/magazine/chemistry-and-the-aquarium-boron-in-a-reef-tank/

In this case, neither of these seems the likely explanation, and perhaps it is just that the CO2 level in the air was higher for some reason the second time, adding more acid (CO2) per minute the skimmer ran. Closed windows? More people around? More cooking with a gas appliance? less obvious situations that impact indoor CO2 are indoor air temp closer to outdoor (less convection)? less windy?

I've actually done a recent cup aeration test and my natural pH balance is around 7.8 - 7.9. So pH dropping was expected. I just would expect it to behave the same way twice.

I'm beginning to think my tank doesn't like to behave as expected...or maybe chemistry laws just don't work consistently in my tank.