I realized tonight that the flow of my filter was down to a trickle. I dont' know how long it's been impaired, it must have taken it a while to get to the point it was at, because I didn't even notice a change. So I opened her up, and started looking for problems. the filter cartridge was in right, the problem wasn't there. I decided that the problem was in the tube. I pulled it out and brought it to the bathroom. Putting it under the faucet, I turned the water on, and this brown gunk came out. It just kept coming, so I turned to the tub for a higher pressure solution. It took about 5 minutes to get all of it out (including frequent taps on the side to loosen it). Filter is flowing fine now. But I'm wondering... what the hell was that stuff? Algae? bacteria? how often should I clean that stuff out? It took six or seven months for it to get as bad as it did.