I have never had sand in any of my Leo's tanks and never will. It's just not worth the risk, it can cause impaction and kill them. The calcium sands are the worst, they do not dissolve (it actually clumps!) and can build up over time...it happens all the time. Since they are made of calcium they actually encourage ingestion, Leo's need calcium so lick it. Leo's lick everything! If any sand is to be used it should be fine, washed/sifted play sand and ONLY for adults, never babies or juvies. Keep in mind though, Leo's don't really live on sand in the wild, it's more of a hard packed clay and rocky area. It's not a natural substrate and can be very harmful in the long run so it's not something I use or suggest using. Nothing loose, stick with solid substrates.