I bought an 18 gallon at *****. It has the same footprint (bottom area) as a ten gallon so it would fit on my old stand and use my old lights (in my freshwater days) but it gives me more water volume for stability. It also has black caulk since the clear type would be stained by medications. I place crushed coral in a large micron bag for stability as well but I can remove it to wash it or if I ever have to medicate with copper.