Thanks Jan.

Assuming it's not live algae (see Jan's test for it again), then you can go to other measures.

I didn't see what kind of filter you have. If you have a sand filter, you can add a little DE powder to it through the skimmer and it may pull out that brown stuff if it's too fine for the sand to trap it. DE is cheap: I'm using the same $8 10lb box for the 4th season now. About 1/4 to 1/3 cup of DE is enough--just enough to raise pressure about 1lb. If you go too high, just backwash and start again.

If you are using a DE or cartridge filter you cannot do this--it does no good on the DE filter and can clog the cartridge filter and damage it.

You should use "Skimmer socks" or their equivalent in your skimmer--they pull out lots of fine, fine stuff. Anyone can use them and they are cheap. I use them all summer but in the late spring and early summer they pull out tons of pollen that we get here in NJ.

If none of these things work, we'll try the next round of ideas.