I use natural red clay in my substrate, root tabs and my lily pots. For just the aquarium based stuff I can get away with whatever small quantity local stuff I can find at craft stores but for the lilies as well I need a bit more. Best deal I've found is here at Axner. $10 minimum order requires 20lbs ordered and with S&H it comes to about $32, about $1.60 per lb. Anyone have a better source?