Canisters trap food particles and they rot. And corals and fish get less food. This may help:
Lots of people want to try saltwater but don't know what to start with, especially with filtration. Here's some options on how to do it:
Super cheap and easy:
1. Keep it simple for your first saltwater tank; you can get more complex later.
2. You can start with a "fish-only" tank, with fake things, and regular “play sand” one inch deep. And one small pump to circulate water.
3. Lights don't matter for fish-only; get cheap, or nothing at all. Fish feel safe in the dark. Or set it by a window.
4. No sump or canister is needed. That's right, no “filter” the way you might think of one.
Thank you, that's very helpful.
5. Feed sparingly, based on the fish you have, and change 30% of the water per month. Yes, this will require new salt (or new saltwater) to buy. But it’s still cheap and certainly easy to understand.
6. Your sand, and your water changes, are your filter!