Question from the Pool School...


Jun 14, 2010
Phoenix, AZ
I just finished reading through the Pool School and I had a question about one statement. On the Definitions and Abbreviations page under dichlor and trichlor is the following line:

"Causes CYA to rise with continued use so it is not a good choice for those with cartridge filters or in climates [...]"

Why are cartridge filters explicitly called out there? I couldn't find any other such reference to explain that in the entire school. I have a cartridge filter, so I'm curious about what makes it unique in relation to CYA.


TFP Expert
LifeTime Supporter
Jan 6, 2010
San Dimas, CA (LA County)
Cartridge filters don't get backflushed. Sand and DE do, so they can count on losing several hundred gallons of saturated water periodically, to be replaced with fresh water, which lowers the CYA.

With a cartridge filter it just keeps on growing

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