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Calcium is gritty and feels alot like sand. It clings to the side - as it gets rubbed off or falls off it settles to the bottom and looks like like tan sand.You don't technically 'get rid' of that, you just sort of put it back into the water by lowering your pH and TA and holding it low for a few days.You also could have water mold, which looks more like somebody dropped a tissue into the water. It floats around, clogs filters, and falls apart if you pick it out with your hand. You get rid of that with a two-step approach: Filtration and chlorination. Chlorine shock the life out it and clean your filters alot for several days.OR,Somebody might have dropped a tissue in your spa - or the label off the underside of the cover, or some other paper thinngy.
Water mold looks like a tissue which has broken up.The labels on some of our covers do tend to fall apart...especially if you have ozone.