I figure this replicates canister filters and picks up the sludge before it can attach to the matrix balls?
The one issue i'm having is filthy filter pads on the 20 gallon long, the floss is perpetually dirty, but the tank is clean and the plants and fish are flourishing. Everything ok with this setup?
So, you have two 20-gal tanks and one HOB filter rated for 30-40 gallons and one 15-gal air-driven filter in each tank. Right?
When you say “filter floss bag stuffed with matrix”, does this mean you are using Seachem Matrix and placing it into a filter bag of some sort? Are you also using some kind of bio-balls? Is the mechanical filtration a floss that you are stuffing into each filter or is there a filter pad of some type?
Might help if you describe the layers, e.g.; water enters a filter pad, then Matrix (or bio-balls), then filter floss (again?), then Purigen.
Broadly speaking, I'm not sure what the intent is to try to make an HOB do what a canister does. The HOB should be fine when used according to directions. It is important to keep the filter clean. I need to clean my filter weekly (29-gal) and, when I do, I squeeze out all gunk as much as possible and replace it monthly.