Wasp this is the mentality of freshwater keepers - I was one of them and still am!
Canisters are equivilent freshwater filters to Protein skimmers. But I have to say, Skimmers are expensive for what they "look" like. A hunk of cylinder plastic put together and that's $500 bucks thanks. :lol:
A lot of expense for Skimmers is the actual pumps. They are special ones which produce tiny bubbles to carry the muck into the waste cup. Both work hand in hand, but if you get a decent pump, then the skimmer will work more efficiently. Correct me if I'm wrong guys.
So Rory, throw away the canister and buy a decent skimmer for the price of a decent canister.
Note: the skimmer in your picture is for a sump. If you are not thinking of getting a sump, then you will need to "purchase" a hang on the top skimmer which are traditionally cheaper, I have one in my sump, but may be moving to a traditional one soon.