I believe that there is a tendency to overstock our tanks with liverock. that is we put in more than we need for filtration. but that aside, you should have as much as you need to get the look you want. i don't know how much i have somewhere over a hundred pounds in a 90, and somewhere near 200 on a 180. a lot depends on type of rock as well, branching types take up more room per pound, which is why i like them more.