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I made my mechanical filter for around $5, after I realized that my bio-filter was not enough for keeping the pond clean, and I was not in the mood to keep cleaning out the pond built-in filter (which is small and clogs easily). I use it around the pond pump (which is a Sunterra 450 GPH pond pump that came with my "Butterfly Garden" kit). I bought a CD-case from Wal Mart for $0.99 and a non-biodegradable but also NOT fiberglass blue flexible furnace filter for under $3. I used some of the scrubbies that I got earlier at the Dollar General for making my gravity bio-filter as well. In retrospect, I would NOT use this furnace filter because the little furnace filter particles get everywhere and every once in a while I find them floating in the pond. I would stick with scrubbies. I didn't use lava rock because I read around on google and it seemed that scrubbies are pretty much the best filter material. It does not end up clogging up as easily as other material may, and is light, and has more surface area. It has been about a month since this got put in and I haven't needed to clean it at all yet.

First I measured the insides of the CD-case and cut a long strip that went from one side, to the bottom, to the other side, with extras hung over both sides. Then I cut two other square pieces to go on the other two sides. I used a lot of yarn and a non-sharp needle special for yarn (which I had from knitting projects) to quickly sew all the pieces together. I wanted to make sure there were no holes primarily because I was planning to get small goldfish later and I was worried they might get suctioned into the filter.

Then I lowered the pump in, and made a cut on the overhanging part for the output of the pump. I padded the pump all around with extra scrubbies, and "tucked it in" using the overhanging pieces. Then I lowered it into the pond.