Yup thats a million dollar question, usually the cycle will let you know when your overloading.
Ive come to the conclusion that pounds of live rock is inaccurate way of measuring filtration. You have to take in to account surface area. One rock can weight 10 pounds and not have the same benefit of a 5 pound rock.
Skimmers, Bio-balls, refugiums, Rock, Sand, Waterflow, Rate of Water Change, Size of Tank, Size of tank mater, Fish Aggression, Territoral Fish, Clean up Crew, Water Temp. are just a few of what has to go into consideration in your tank.
I will have 10 in tank when completed. All peaceful.
Clownfish x2
Mandrain Dragonet (Spotted and Psychedelic)
Copperband Butterfly
Coral Beauty Angelfish
Firefish (Regular & Purple)
Bicolor Dottyback
Sixline Wrasse
Midas Blenny
Comes to about 36 inches fully grown, so if I went by the inch per gallon rule i would be in trouble. Everything gets along good now i only have to add 3 more of them to the tank.