But is it a general rule that you need 1 lb per Gallon? Why is that then? If a 2lb solid rock has the same surface area as 1lb porous rock, then which one is better? it would mean that the porous rocks will have more surface area then the solid live rock. A 20lb amount of solid live rock will have less surface area than 20lb of porous rock, so that said, is getting porous better 'cause you have more area for algae to grow on?