small pond filter
As promised here are some pictures of my filter and some basics on it's design.
First here are the pics:
http://new.photos.yahoo.com/cmslick3/album/576460762403566822
Let me first tell you that I had a problem with dirt seeping from my planters into the pond so the filter picture is before I changed to rocks for the planters and vacuumed out 75% of the water and mud. As of today the filter has been going for 2 days and is no where near clogged.
Basically I bought 2 whole house filters, 2 4' foot lengths of 1/2" PVC, 1 4' length of 3/4" PVC (for inside filter housings), 8' of vinyl tube to fit pump output and filter input/output, as well as various elbows and threaded ends etc... Unfortunately it's not a one size fits all application, so you're going to have to make it fit your needs.
I put the input to the filter in reverse of the flow indicator on the filters so that the water would come in the center and out the outside. Normally it goes the other direction since that's the way the cartridges are designed.
I cut the tubes inside to fit firmly into the guides that exist for the normal cartridge, however they need to be slightly longer than the actual cartridge. If I remember correctly I ended up with 10 3/4" and trimmed down from there until I got a snug fit. I also used a piece of airline tubing to create a seal in the top and bottom guide, i think they were roughly 2 1/2" long and I shoved them into the channels with long screwdrivers. This insures that the water does not bypass the filter material and keeps things flowing smoothly. The holes on the bottom of the tubes are 9/16" which seems to be plenty of flow, believe me I went through multiple attempts before coming to that size. Also don't put them at the very bottom, you need about 1/2" offset.
The first chamber is the mechanical filter, and the filter material is offset from the bottom of the chamber to allow really big stuff time to settle. I also think this helps to reduce the pressure put on the water and allows more to be caught. My material of choice so far is round plastic pot scrubbers, a whole DOLLAR for 12 of them, I only use 9 and a bit of polyfill in there so it's quite affordable. I found that stacking 6 scrubbers, then poly, then 3 more scrubbers seems to work well. I don't put the poly at the top because it tends to come lose and clog the output of the chamber. Feel free to experiment with this.
The second chamber is basically the same except it's got a put scrubber on the very bottom, then marble sized pieces of lava rock to the top, finished with another put scrubber.
I can't think of anything else, unless there are questions.