Quote Originally Posted by DCR
I have an 18 AG that I maintain using the BBB method that I have learned here. I have been guiding 3 families using the methods I have learned here. All of them are the happiest they have ever been with their pools.

Three of the pools loose about 1-2 ppm cl a day while the other looses 4-5 ppm per day.

His numbers are

cya 40 ppm
alk 180 ppm
ph 7.8

All of the pools have similar numbers. The only difference is the pool with the high cl demand is in full sun all day, and the others are partially shaded.
I believe you already partially answered the question. Sun depletes the cl. The cya helps to prevent the loss but loss is normal. 4-5ppm seems a bit high though. Do you have combined and free cl levels by chance? Also I would double check the cya reading. At 40 the cl should not drop that quickly. Alk and ph are a little on the high side but I am not sure if they would have that great of an effect.