Well Kurt's data shows that it is definitely the outgassing of carbon dioxide that is going on, at least initially. If the SWCG system were somehow introducing base into the pool, then that would increase pH and TA such that adding acid would get you right back where you started with pH and TA. Instead, Kurt's data shows a steady decline in TA at the same "target" pH.

Interestingly, Kurt should be seeing a slow down in the amount of pH rise and acid demand as his TA is lowered, but I don't see that from the data. He is also now in the "green" region though still out of equilibrium with over 5 times as much carbon dioxide dissolved in the water as is found in air. If he reaches a state where his TA does not seem to be lowering (and it looks like this may now be the case, or close to it), but he still needs to add acid, then something in the SWCG system is indeed adding base (and was earlier too, but was masked by the CO2 outgassing).

There are several ways that an SWCG system can add base. The simplest is having the generated chlorine gas not dissolve completely into the water since the conversion of chlorine gas into HOCl is a highly acidic process that partly compensates for the highly basic process of hydrogen gas production. The difficulty in detecting this is that you will find bubbles of hydrogen gas flowing from the salt cell into your pool and you can't easily tell the difference between hydrogen gas and chlorine gas except possibly a smell of "fresh" chlorine.

Great data collection Kurt! Keep it up.

Richard