After a year of crystal clear water and no problems, I got sloppy and didn't check the FC level for a week. We had opened with FC=12.5 and perfect water, but now we had cloudy water – not green, just white/gray cloudy. My fault. So we started to SLAM (I've done it before so I know it works). As the water cleared a bit, I detected some black and mustard yellow stuff on the joint between the light lens and the chrome ring around it. I brushed it and it became a fluffy cloud that floated away. So we took the light out, scrubbed it above water, and scrubbed out the housing. It was full of black flaky stuff that floated to the floor of the pool. We continued the SLAM, and raised the FC to the mustard algae shock level of 40 for 24 hours. When the water was clear, I did the OCLT (SWG off) and lost nothing overnight, so I've been letting the FC drift down for several days. It was at 17 last night – I did the OCLT again just to be sure, and it passed again, lost no FC, CC=.5, water clear. But this afternoon, the fluffy mustard-yellow stuff is back on the light. Help!!