I have a in ground pool, ~13,000 gallons, about 10 years old with pebble tech finish. It has a spa that spills into the main pool. I've always kept the alkalinity level between 80-100 for my SWG. During the last 2 months, we had some heavy rains that lowered the alkalinity to ~40. When checking the water chemistry, I saw that the pH was only 7.4. Also, since I usually add liquid acid once a week to keep the pH in the acceptable range, constantly adding acid probably help reduce the alkalinity also.

Hum...that is weird because I usually have to add liquid acid one a week to keep the pH in the proper range. So I ignored both values and waited another week. In the next test, the pH only rose to 7.6, and the alkalinity remained at 40.

So now my question: why would they recommend to have the alkalinity at a higher level, when it causes the pH to raise significantly in a week? According to the mfg of the SWG cell, the recommend range is 80-100.

Current readings today using a Taylor test kit (the one with the powder for CC count)
Water temp: 68 F
FC: 2.6
CC: 0
pH: 8+
TA: 90
CH: 425
CYA: 80
Phosphate: 0
Salt: 2200 (normally at 3000, but due to rains, was deluded somewhat. Okay because my cell is not connected during the winter months - I use a bypass and liquid chlorine during this period).

So come next Sunday the 15th when I check the water again, I expect the pH to be back up to 8 after adding acid to bring it down to 7.2.