PFS doesn't have chemicals in it. How much does it cost to ship a bag of sand? PFS is #20 grit sharp sand, usually silica, although it doesn't have to be. Surely you can get some of that closer to home, like from a sand blasting supply or construction supply if not from a pool store?
50 lbs will be just enough.
Join a fish club. Don't have one in your area? Start one.