i use 3m color quartz aggregate in the "t" grade. its quartz coated with ceramic. its guaranteed to not leech or bleed 3yr warranty. also it wont fade,heavier than sand and wont syphon up during cleaning. makes my tank look like i clean it daily. cost me 30.00 per 50lbs. bag at my local pool contractor. they will even send you samples of all colors and grades free! i through in some 2" black mexican beach pebbles and larger rocks to make them happier.