I just replaced most of my southdown sand recently. I was too fine. I could never get the right flow in my tank. I replaced it with seaflor special grade reef sand. this stuff is great. the grains are just the right size. I now have the flow I want without having a snowglobe tank. this sand is available at most lfs or online, it's about $34.00 for 40lb bag. I wish I used it in the first place.