It depends on the density of the rock .... I have about 16 pounds in my 10 and the 2 clowns still have room to swim around. If it works and you like it, go for it.
I agree with bigarn..
I dropped 7.5lbs of Marshall in a 10gallon today and I don't have much room for anymore..
You don't want to overfill it and not be able to do routine maintenance and stuff...
