Small, 3,500 gal Intex above ground pool. CYA is 88ppm and pool store told me to drain and refill. Hubby says it's not necessary to do that and it won't hurt us. I shocked the pool in the early am before the sun got bright then took a sample in to have it checked. Pool store clerk says it's to out of balance to test until the shock gets to work but that at 88 ppm I need to drain some water and refill.
We changed out the cartridge filter to a Hayward sand filter this season.