I used to add some to the filter line to create a "floc" on top of the filter sand. Find crud would be caught, and the filter cleared by backwashing.
I don't know if it's still used, or whether what one might buy in a pool supply place would be OK. I'm not familiar with using it to precipitate silt, only as a filter layer.
Kayak & Canoe Outriggers
Free Standing Boat Racks
Classic Freestanding Rack
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