The difference between pool filter sand and regular sand is the size of the granules. The sand in a child's sandbox, for example, is much coarser, measuring up to 2 millimeters across. Pool filter sand, in comparison, is much finer, at just 0.4 to 0.55 millimeters in diameter
Most average sized Sand Pool Filters will need about 3 bags of sands. But if you can't figure out how much sand you need, just fill your tank until the sand reaches about 6 inches from the opening. Fill the tank with one bag at a time.