Greaser and algae, thanks for your comments.
Greaser, I used to feel that way until I realized you can't control it. I've had everything from planaria to Copepods, nematodes, hydra and the like. Once you fight the forces of evil planaria, you come to appreciate the simplicity of snails haha.
Algae, you might put a sponge over your intake. I don't find I've had the issue of them dying in the back of my canisters.