Cleaning sand is a hassle but it can be done. Fill your tank with the sand about half full, stir the snot out of it with GLOVES, let the sand settle then siphon the dirty water. It will take several times to get it cleared up. Since your tank crashed before, I would not recommend using or even cleaning the sand, get rid of it. Buy a bag of aragonite sand, a rock or two and start your new reef on it's way! TinMan