If my pool is covered all day it is fine, but when I pull the solar cover and leave the pool exposed to the sun I'm losing a whole lot of FC. Yesterday morning 7AM FC was 14.5, in late evening it was 9 FC. The SWG ran 12hrs. at 70% and it is oversized. I preformed the OCLT test and it passed with no problem. I had algae about 3 weeks ago, and I slammed the pool, and kept it at slam level for several days and passed the OCLT test then. Water looks nice and clear right now. My guess is algae, but why am I passing the OCLT? Could there be anything chemically that would cause this?