if you go with sand, you can use pool filter sand, or believe it or not, play sand. just make sure to wash either off thoroughly. and this coming from a guy who rarely rinses his substrates. i have used both, they are pretty much equal, but the pool filter sand depends on locality. some are tan, some off white and some stark white. i always make sure to "accidentally" poke a hole in the bag with my keys at the pool supply place so i know what color the sand is....LOL the one true downside to sand, whether it is the ones i listed or the overpriced aquarium versions, over the course of time, a long time, it will compact. this isn't much of an issue unless you are using it to cap dirt. eventually, the sand will sink into the dirt and the dirt will start to rise. also, when planting into sand capped dirt, it makes a mess when removing plants. so if you go with sand, make sure you are happy with your aquascape the first time