Hi all, Haven't really posted much lately. I recently upgraded from a 36 bowfront to a 40 breeder, and decided I also wanted to upgrade filters. I received a very old fluval 403 canister with the tank, and it ended up breaking. I went out today and purchased a new fluval 306 canister, and have it all set up. I have kuhli loaches, so on my old tank I'd use pieces of sponge over the intake end. I noticed inside the intake piece there's a check ball. I'm trying to figure out if this will keep kuhlis from swimming up, or whether I should find a bigger sponge for the intake?