I have a 15,700 gallon oval AG pool with vinyl liner. I have been using TFP methods and pool math with my TF-100 test kit. Thing going great since start up this year. Chemicals are spot on FC 1 PH 7.4 TA 100 CYA 30, I put recommended borax and bleach in like normal to bring levels to normal and the water is clear but there has been a fine "dusty, silt-like" film on the bottom stirs easily, not slimey or green. It will vaccum but takes forever and is back the next day. What is it? How do I get rid of it? Do I need to add clarifier or algecide. Please help!! I have a 1.5 hp 1speed sand filter, thank you