I have always had issues with the filtration on the 300 gallon. For some reason, the pond bead filter just doesn’t seem to perform the way it should. The water has always had clarity issues from particulates. This has been extra frustrating because I am so used to working with canisters and have never had to deal with inadequate mechanical filtration.
When the water first entered the sump, it entered a section about 5″ wide or so with a foam block in the bottom that the water had to pass through to get to the K2 tumbling media section. The problem was that the foam block would become saturated pretty quickly and then the water would bypass the foam block (within days).
I ended up removing the first baffle and installing a plastic 3-drawer organizer raised up by PVC pipes. I cut the bottom out of two of the drawers and put eggcrate down. This way, the media is held up by the eggcrate, but can still drain very easily. I skipped using the third drawer just because the water level in the sump is too high and it would be submerged.
I am now experimenting with the best filter medias. I started with just some polyester quilt batting, but this was clogged up in about a day. I have also tried a dual density filter pad, but the finer section was too fine and also clogged up very quickly. Currently, I have some course foam in there that is approximately the same pore size as the foam block I had before.
I think the basic design I originally had works well in general, but on a 300 gallon tank with a lot of community fish and some very large fancy goldfish, one foam block simply wasn’t enough. Perhaps a wider section with three or so foam blocks laid side by side would work while not clogging in less than a week.