Build-up by returns, don't think it's algae

[flygirl516]

Hi all,
I seem to have a build-up of tan/white clumps under the returns in the pool. I don't lose any chlorine overnight, CC is 0, and it's nowhere else in the pool. When I brush, it "poofs" away and dissipates. The rest of the pool is clear and nothing is kicked up when I brush.

We replaced our sand filter this year and it has new sand. I've also added DE occasionally to get rid of the small particles (we had a lot of pollen), but backwashing should have gotten rid of the DE. I SLAMed for 2 days, passed OCLT, did a mustard algae SLAM for 24 hours the other day too in case it was that, because it had the yellow-ish tinge, but it came right back under the flow of the returns only.

Any ideas what it could be? Perhaps very fine sand particles? I'm considering just vacuuming it to waste.

 

[Texas Splash]

Have you been able to collect any of that debris that is falling under the return jet? It would be good to see if it's gritty like sand or smooth like some sort of organic product. Maybe secure a sock over the return jet to get some?