you wana get whats called Yardright playsand, but i see youre from CA
like me and its not gona be easy to find it in CA
. You can use quikrete sand which is silica altho some go against it i know ppl that use it all the time with no problems. You want small sugar sized grains. If you have a large tank then a 50lb is worth it but if you have a small tank or nano id say just get some from a lfs
and no deal with trying to find aragonite southdown sand.