welcome lexuslan!
I think what the other have said will work best for you with the batting. But no need for the headache of putting it in the fillters you have, (plus you would have to clean it more often and best to leave the bio part of your systems alone if at all possible) I would just do as Sissy has shown you and the others have said, most the time the simple things do the work better and faster..
I use and old small laundry basket, line the sides so the particles do not escape through the holes ( the little stinkers! lol), and put a couple more layers in the center ( dont fill it with too much because the water will not have time to filter through and will spill over). Looking at your waterfall, I believe you would have room for a small-ish crate with holes in the bottom, like the one sissy uses, and just simply place the crate on the waterfall, put the hose to that side of the waterfall into the batting lined crate.. in no time at all you'll have a much clearer pond and no headaches with plumbing. Just rinse and repeat as needed! Lol ! The first time I used batting, I bought a huge teddy bear at a yard sale for 10 cents and used the stuffing out of it... Worked great!! And Cheap Lol !!
Also, maybe i missed it but, do you have a pre-filter after your pump and before your bio filters? If you do Not, this would be a big help in keeping your bio filters cleaner and in turn your pond as well.
sorry, have a tendency to be long winded at times
but I'm harmless
Good Luck!