Quote Originally Posted by Rangeball
I tested PH again last night. 7.8. I couldn't believe it, so I checked again. 7.8. Tested Alk, which was down to 100.

What would I have to get my alk down to to get PH to stabilize at 7.5?
Take a look at the CO2 outgassing chart I made. You were at a pH of 7.1 with a TA of 110 before the kids came over, but as I mentioned, the relative CO2 outgas rate of 28.5 was quite high so I did not expect that to be stable.

Now you had lots of aeration and your pH rose to 7.8. Technically, the alkalinity should not have dropped until you added acid, but ignoring that you are now at a relative CO2 outgas rate of 4.1 which is very stable. In fact, it is surprising that your pH didn't significantly slow down its rise at around 7.5-7.6 so the amount of aeration in your pool must be quite significant (pretty vigorous splashing! maybe some high winds too).

So whereas I initially would have said that you could stabilize around a pH of 7.5-7.6 with your current TA of 100-110, given your significant aeration situation I would say that you would need to get your TA down to around 60-70 to get more stable. Even then, you may still find the pH rise with your kids splashing, but it should rise less and the amount of acid you need to restore the pH should be less. Of course, getting your TA that low with the fill water you have to add may be quite difficult and you may have to live with some intermediate level, but that's up to you.

This rather low TA will make your system bounce a little more in pH from external sources such as adding acid or adding chlorine, but it is still reasonably buffered (it wouldn't be good if you were using Tri-Chlor tablets, for example, due to its acidity, but we all know that Tri-Chlor isn't good for other reasons as well).

Richard