We just bought a house with a small pond in the backyard. It is one of those with a medium-sized pool up high, water-falling through 3 small-sized pools to a large-sized pool at the bottom. All pools are the black plastic. There is a small fountain with its own pump in the bottom pool, as well as another pump that recirculates water back to the top pool. We tossed about 6-8 little goldfish into the bottom pool and there is a large watere-lily (I think) in the bottom pool. My problem is that the filters on the pumps keep clogging with, well, 'sludge'. My wife spent one day cleaning out most of the water before we moved in--it was filthy. The fountain has a filter about the size of a Coke can that looks like a sponge--it only takes about 1-2 days for it to completely stop flowing water. The other circulating pump looks smaller, and has no filter--it just fills the pipe running to the top pool with 'junk' until it almost stops (takes about a week or so). How do we combat this? Do we need a large circulating pump to an external filter or what?