i have a 2222-37 eheim canister that i have drug out of retirement and trying to bring the seals back to life (the large one being $20 plus ship) but i want to put charcoal in it and the holes in the tray are to large for the charcoal that i have. can i cut a piece of new fiberglass screen to line the bottom of the tray to keep it from falling thru or do i need bigger charcoal pieces?