We have a backyard pond that's about 10' x 10' and about 3' deep and it has a running waterfall. We have a large biofilter that's connected to a new pump. Everything has been working great for a long time, the old pump and even the newer pump. It always took about 5 to 7 days before we would have to clean out the biofilter to get it running full speed again. All of a sudden, though, we're having to take out and clean the biofilter literally every other day. The first day it's cleaned, the water flow is powerful. By mid-day the following day, it's barely running, so has to be cleaned again. The strange thing is that when taking apart the biofilter, the sponges inside are not even dirty. They have a tiny amount of sludge, but mostly clean. We took it apart and couldn't find any blockages, cleaned out all the hoses, and also took apart the new pump. We cannot find any reason that this might be happening. It doesn't make sense that it runs at full power after cleaning, then the next day is just about not running at all.

We tried putting the biofilter inside of a tight mesh bag, but unfortunately, a couple of the fish (Koi and Goldfish) got their fins stuck in the mesh, so we had to rescue them and cut the bag apart. Of course we are no longer using the mesh bag since we don't want the fish stuck and/or injured. I really don't think sludge and debris are the issue since the parts are pretty clean when we take them out to check them. We also totally clean the pond every several weeks, taking out all the fish, draining all the water, and completely cleaning the liner, etc. So the pond is pretty clean and well taken care of.

Both the biofilter and pump are the same brand and everything fits together perfectly. Biofilter is the Laguna PowerFlo underwater filter with 5 or 6 sections and the pump is the Laguna MaxFlo 2900.

Has anyone had a similar issue? Does anyone have any idea what could be causing the rapid slowdown?