I got tired of paying 3 bucks a filter for my whisper 5-15 fish filter for my sons goldfish and the filters are becoming harder to find in the area I live in so I decided to make my own for what I later figured to be less then 15 cents a filter. Im sure this same methode could be used on other like filters/pumps that use this same style filter as well, you will just have to adjust size and fit.
Step 1: Make a Frame
The replacement filters I have been buying didn't have any internal support. Some of them do and some of them don't. The last one I had did not so I had to come up with some sort of internal frame for the new filter. I found that a light switch cover to fit perfectly.
Step 2: Cutting Frame
Now some light switch covers are made from a hard plastic and you wont be able to cut them with a razor knife without cracking. The one I had in the garage was made of some sort of soft vinyl and I found I could cut it very easy with a razor knife. I cut it so there was about 1/8-1/4 inch of plastic left all the way around the edge. You might be able to buy a one of those square light switch covers that already have a large square hole cut them in or maybe even use a plug cover and break out or cut out the center piece. Whatever you use make sure it will allow for the most water flow for best filtering.
Step 3: Test Fit
Test fit in the pump housing.
Step 4: Cutting Filter Material
You have to get some polyester fill batting. I got this 6 foot by 3 foot roll (actually its about 9 inches wider then 3 foot) at Hobby Lobby for $6.99. I figured I can make something like 255 filters out of this. There are different thickness of this stuff. I bought the 1/4 inch thick stuff. I doesnt look to dense and seemed about what the old filters where made of. Cut a piece of the batting so that it folds around the filter like in the picture. I cut mine about 1/8-1/4 inch larger then the filter frame. This will allow some space to glue the thing together.
Step 5: Glue It Together
Then glue it together with hot glue. Glue 2 of the 3 sides. I left one of the ends open for the next step.
Step 6: Test Fit
Test fit the plastic frame.
Step 7: Fill
I used Zeolite to fill the inside of this filter. Zeolite absorbs the dangerous ammonia that fish and food waste create. You could use activated carbon or a mix of both. I happen to have zeolite from our turtle tank filter so I used this. I used about 2 table spoons full inside the filter. Thats just a guess based on how much carbon was in the old filter. You could add more if you had larger fish or more fish in your tank.
Step 8: Seal and Install
Seal the last side with hot glue after filling then install in the pump. Including the zeolite each filter only costs me about 14 cents to make and about 5 mins worth of work. When this gets dirty just cut off the poly fill, dispose of the zeolite and make another filter using the plastic frame.