I have been getting a yellowish substance in my pool that is VERY easily swept/vacuumed up on a consistent basis the past month or so (every week and a half to two weeks). My levels are perfect - I even brought a sample to the pool store and their readings matched mine. When this shows up I usually brush the pool, let the skimmer and the barrucuda do their thing, and all is fine....till is shows up AGAIN. The chlorine levels are fine, like I said ALL is perfect but this keeps showing up regardless. Could it be yellow algae? Or could it simply be dust? We had a new roof put on just a few weeks ago but the dust from that was a red color, I can't imagine it's that. But I don't know that this could be algae if my chemical readings are fine. HELP! Any ideas?