Actually the ratio depends on the type of rock you have and the porosity. South pacific rock, ie. marshall island, fiji, kaleani etc are very porous and have a lot of surface area per pound so you can therefore get away with fewer pounds/gallon. Caribbean and some base rock is very dense and heavy and therefore you need more per gallon such as up to 2lbs/gallon. I have 14lbs of marshall island in my 75 and it is quite full.
Panther, glad to see the rock is helping to clear it up.