I was able to use the fantastic advice learned here last summer to turn my slimy, green pond into a sparkling, clean swimming pool. I gradually got the CYA level up to 95 by Sept. to stabilize chlorine use. I only tested FC & pH over the winter. All was well until last weekend when we got such heavy rain that it flooded my pool with dirt & debris. It took a few days to get the water clear again. I decided to do a complete test with these results: FC=8, pH=7.4, TA=70, CH=310, CYA=33. What happened to my CYA? I thought it could only be reduced by water replacement?