I purchased a tunze 9010 about three months ago... it is in a FOWLR 90 Gallon, and runs well... my question is, should i just be getting a thick black pudding like substance on the INSIDE of the narrow part of the cup leading toward the top, or should i be getting many cc's of dark water in the collection cup? Right now i have to wipe out the inside of the tunnel daily to get out this black sludge, but i do not get many cc's of water... the bubbles are breaking at least halfway up the collection cup. Bunker