I've used crushed coral and also sand. Should your going to use sand get numerous snails to keep it thoroughly clean, you don't need to be vacuuming it or stirring it up,it make a mess!! Now if among the list of 4 corners of your aquarium stand is decrease or https://aquariumsetuptips23811.mdkblog.com/43369299/the-5-second-trick-for-aquarium-setup-tips