Here is a better picture of what I now think is probably definitely mustard algae:



If you see my thread a few posts down, we originally concluded it was settling dust in the crevices of the wrinkles where the foam under the liner was. However, this picture is after a week of no use, no vacuuming, but still maintaining chemicals. As you can see, water is crystal clear and perfectly balanced. But the "mustardy" color is worrying me now. My vacuum hose broke so I need to get a new one to sweep this up and I guess I will have to superchlorinate. Is that the way to get rid of mustard algae or do I need to buy something (gasp!) from the pool store? Thanks all!