Recently set up a 30g Oceanic cube, drilled with a sump. I put a Coralife CSS65 on it. The first 6 weeks it pulled black gunk out of the water while the rock cured. I have since gotten some zoos and one fish. I only have 25g of water total and I do a 5g water change weekly. The skimmer is not puting out anything. Could I have gotten everything out of the water that there is to get out? Can you skim a tank to the point where you won't get anymore out?