Planted Tank Guru
Join Date: Jul 2010
Location: British Columbia, Canada
Most PF sands sold @ pool supply stores are graded #20 -#30 in density which is good as a substrate use. You don't want the sand to be too fine, as it would easily get disturbed & free-float into the water column, clouding water and making it get readily sucked into filter intakes, & clog up impeller assemblies. Also it's difficult to vacuum properly and a lot of it would get siphoned up, eventually needing replacement.
Also, being finer-sized, it compacts more readily & may cause problems with potential development of anaerobic gas pockets.