use to be a recomendation 3-5 lbs per gal. somthing like that. after 2 yrs. of too much rock and too many dead spots (even with a ton of flow) I took out all my rocks and cleaned them and the sand bed. What a mess. then I raised the rocks off the sand bed and left 40 or so lbs out. It's like a different tank.hair algae almost gone. all corals opening up fully. rocks look clean as does the sand bed and it will be so much easier to keep it this way.