Did you drain the pool at the end of last year? Have you used trichlor all of last year and pretty much exclusively this year? Trichlor is stabilized meaning it has CYA in it. Continuous use of it causes CYA levels to get high and as a result, it is necessary to run higher than normal chlorine levels to keep algae away. (See the Best Guess Chlorine chart in my signature below for more about that.)
Do you know your CYA level?
What kind of kit are you using?
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