Hi Tom!

Your problem is a universal one , and has to do with the fact that, as ponders, we deal with living systems. The combination of fish, plants, food and sun generates organic byproducts (s**t) plus dirt and sand. This is your sludge. Your problem is twofold. First, you are running a heavily-populated pond without a bottom drain. I'll even bet that your pond's bottom is covered with rocks. Sludge is unavoidable, and if you are using a submersible pump, the pump is pulling up the sludge, homogenizing it and shooting it directly into your filter. Under these circumstances, fouling is inevitable. A bead filter run with this system will foul just as quickly as what you have now.

The best solution for your pond would be to place a vortex or other prefilter between the skimmer and your pump. The prefilter (something as simple as a big box with offset baffles and a sloped bottom with an outlet valve) set at pond level and gravity-fed, will remove the larger suspended particles. The partially cleaned water can then go to the pump and from there can go to whatever filter you prefer. Next in line would be your UV and from there back to the pond.

As far as what kind or size of filter you need, you need to get to a fairly large Koi Show where a number of dealers and manufacturers will be present. KoiAmerica or the MAKC show would probably serve. Our koi show does not have a large number of filter manufacturers present, but we've got a lot of experienced ponders.

Happy ponding!

Bob