I went to Leslie's Pool Supply and picked up some 20 grade pool filter sand that has a warning on the back that it contains crystalline silica that can cause respiratory problems if you inhale it. I had heard people recommend that this would make a good substrate for tanks and would like to switch to it in the near future if possible (my current substrate is mostly jagged rocks and my leopard ctenopoma likes to scavenge through it with his face and gets cut up). My question mainly is if the crystalline silica is toxic to the fish and if the substrate is safe? Any other tips are welcome too.