I'm completed my mods for the filter and I'm happy with the results:
First, I removed the bottom foam, because it just seemed pretty pointless to have it down there...seems to me that water flow through this would be pretty minimal, especially with the intake so high up.
Then I used 2x 3/4" PVC elbows (about 80 cents each at Menards)...one female/female, one female/male to create a "U". I attached an intake from a biowheel 300 filter to one of the openings and shoved the other over the pump intake. I used a left over "O" ring from the return tube over the pump intake to make it a a more tight fit (or the 3/4" elbow would have been very loose on there.)
I filled the bottom area with nylon netting (from garden supply shop) because I cannot find "pot scrubbies" anywhere. This stuff is cheaper anyway and is real easy to fit in irregular shaped spaces. I believe this will allow for additional surface for bacteria w/o blocking flow like the sponge would. I also placed a good size bag of carbon down there real close to my intake, so it gets reasonable flow. I then plugged the big hole in the top sponge with more nylon netting to prevent the water from short circuiting/bypassing the filter foam.
The point of this mod is to force water to flow from top to bottom of the filter, instead of the stock design which starts to draw water into the pump about 1/2 inch down from the top, leaving the bottom half of the media pretty much uncirculated.
Here are some pics to show the details:
here are the two elbows and the intake strainer. I was planning on building my own strainer, but I had this laying around and it worked so perfectly, that I didn't bother. otherwise you could use 3/4 inch pipe and cut slots into it.
This shows the whole assembly with "U" and strainer in place. The bottom of the strainer is resting on the raised pegs of the bottom of the bucket about 1/4 inch above the floor to allow proper water flow.
The bottom area is filled with carbon/nylon netting.
Top sponge in place. I cut a small slit into the bottom side of the sponge, so it allows the raised "U" tube to fit in there...the sponge sort of hugs it and curves around it.
I plugged the hole with nylon netting to prevent bypass flow.
This mod was super easy to build and very cheap. I have been running the filter this way for a few days and while I never actually measured flow rates, it seems very strong. The filter is rated at 550gph and it looks to me like it's putting out that much with media in place. I'm running this filter on a 155g bowfront with 3 oscars.
Questions or comments are welcome!