There are many reasons people use Pool Filter Sand, myself included. When you get it, clean it. I pour some in a 5 gallon bucket, stick a hose down in it, and let water run through it and out over the top of the bucket to clean. Really simple. Do this until the water runs clear enough. Then put it in your tank, and start another batch using the same technique, until you have the amount of sand you want in your tank. One 50lb bag of PFS is 10 bucks approx., and it will cover a 55 gallon tank by about one or two inches nicely. Get two bags if you want 4 inches.