Hi - thanks for the response.

I have a cartridge filter, Hayward StarClear Plus C1200. Just added pool details to my signature.

Pool is a pool-spa combo where the spa is in one corner, raised up, and some of the returns go into the spa which overflows as a 2 ft wide waterfall into the pool, so the water is constantly aerated. Also have a blower for the spa if additional aeration is required.