a half pound per gallon of water is all that is needed for bio filtration.
Why do you think so many places "recommend" 1-2 pounds per gallon? Ill give you a hint, it rhymes with honey. :eek1:
For example if you got a 100 gallon tank, 50 pounds is all that is necessary(give or take a few pounds as stated depending on porosity)to properly filter the tank. Now 50 pounds may not be aesthetically pleasing to your eye and you may want more. Thats fine, but not necessary at all. Some people like to look at a wall of rocks, some people dont. Thats called personal taste.