Interesting finding concerning pH...

[chem geek]

Also, if you have short pipe runs from the SWCG to the returns in the pool, then if the chlorine gas doesn't all dissolve in the water and some of it outgasses instead, then that also contributes to the pH rising. If 40% of the chlorine generated by the SWCG were to outgas, then that would completely account for the amount of acid you had to add, but the TA would not drop in that case. If 0.7 pounds of carbon dioxide were to outgas, then that too would completely account for the amount of acid you had to add and in this case the TA would drop by 7 ppm. You may have both of these processes going on.

Note that your FC of 2.5 ppm is too low for your 80 ppm CYA. I'd get that up to around 6 ppm if you are manually dosing. When you get the SWCG back in operation, then the target would be 4 ppm assuming it can be maintained stably.

[steveinaz]

Note that your FC of 2.5 ppm is too low for your 80 ppm CYA. I'd get that up to around 6 ppm if you are manually dosing. When you get the SWCG back in operation, then the target would be 4 ppm assuming it can be maintained stably.

Yep, I'm aware--just doing the minimum as my SWCG gets installed Tuesday.