In my 180 tank there is about 4 inches of sand. In my refuge I recently took that magic mud out (it was really old and the LFS didn't carry it) and I replaced it with crushed corral. Now I am reading that I probably should have put sand back in there if I was going to put anything back in there at all. I dont have extremely high nitrate levels but it is no were near 0. Ive been changing about 20 gallons of water every other day and the levels aren't really dropping. If I put 6 inches or so of sand in the refuge will this help at all? Or does the DSB that im reading that helps people with nitrate levels only work in the DT>