Whatever sand you are using, it needs to be coarse, not fine sand. If I remember correctly, pool filter sand is fine sand. It is coarser than play sand, but still too fine to use in an aquarium. If you can find a silica sand that is cheap and coarse, then use it. I still would recommend gravel in the .5mm-to-5mm range, but if you are committed to using sand, use the coarser grades.
Cats: Small quadrupedal mammals that share our passion for fishkeeping, although for somewhat less then altruistic reasons.