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.Originally Posted by DCR
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