I tried an experiment to set a skimmer extremely low in a the system with 400+ gallon system. For several month, I did not get any skimmate out of the skimmer, basically it just bubbling in order to saturate the water with oxygen for the fish. Coral are growing faster. May be skimmer is really not that critical for larger system with large amount of live rocks. I also notice the growth of fan worm and sponge is going crazy too. Just a thought