I've got a 30 gallon thats been set up for about 9 months that has about 4o pounds of live rock and a 3 inch sandbed. The only critters are a cleaner chrimp that I put in tonight and about 25 bluelegs. There hasnt been anything in it for about 6 months so no waste is being produced. Recently I put on a red sea HOB berlin skimmer. It was pulling foam the first night but after that nothings been coming out. Can it be so clean it cant filter anything?