I'm just reading my way through Delbeek & Sprung's 'The Reef Aquarium - Vol 1' - absolutely awsome book packed full of information. They have basically pulled together a wealth of research and added their experience about everything reef-keeping. It's taken me a while to get to reading it, but I highly recommend it!!! anyway, I just read a section on Protein Skimming and they recommend cleaning the cup & 'neck' about once a week. They also explain that it is very important to keep the body (inside) clean, recommending that you make sure a transparent one is not exposed to light to reduce the build up of algae etc on the inside & cleaning it once a month! I have never cleaned inside mine, and had put decreasing performance down to other things (pump etc)... I now plan to keep mine clean.
