I've had my FC levels at 40 for the last week. CYA is 50, pH is 7.8. I can't get rid of what I thought was mustard algae. I pass the OCLT. The pool is clear. I brush and backwash, but within 24 hours it's reappearing on the bottom, never the sides. I have stuck a water hose in my sand filter, to declump any clumped up sand, but that didn't help either. Any suggestions?