Hi there, though I do regular maintance, I'm no longer getting "nice" dark liquid from my Tunze skimmer. A lot of foam is produced which is constantly flowing out of the cup through the small holes which secure the lid. I've tried regulating the air (i.e. putting to bare minimum to half way), but I only get "pale" liquid - very watery. Could this be related to the quality of the water (I've been figthing an outburst of slimly alge for the last few weeks). Any advise?