I believe most playsand is silica. However I think in the end you'll spare yourself a lot of time and aggrevation by driving the extra distance and paying a few bucks more for pool filter sand. Play sand is much finer and lighter per grain which means it takes much longer to clean and doesn't settle as well under water. The finer grain will help to eliminate anaerobic pockets, but will also require more sand to get the same substrate depth. That fine sand will get into filters and powerheads, shortening their life span, and if you have any fish that dig expect your water to be a lot more cloudy. Just my 2 cents: you may save yoursel a drive now, but every time you clean it later its going to aggrevate you.