I have a brown powder type substance gathering in the seams and corner of the pool. The pool is in total sunlight with very little shade anywhere. The pool will look clean but when I brush it I can see this stuff cloud up the water. Therefore I started to SLAM. My CYA was low so I kept it low to SLAM. started this last weekend and kept FC levels 14 ppm or higher until 3 requirements were met (which only took 1 day) current test results are FC 10, CYA 30 (kept low for SLAM), pH 7.6, TA 70, CC 0. Water is crystal clear except the stuff seen in the picture. So the question, what is it? I don't think it's pollen because it was there before the pollen appeared this year. It doesn't feel like sand and disappears when brushed. Thanks for the help.