I've just added one of these to my filter system. It goes between the canister filter and the intake so it catches all the big gunk before it gets to the canister and dirties it up.
And the best part? It's a by-pass, so you simply turn the black top 90º and you can remove the bottom to clean/replace the cartridge - without having to turn your filtration off! The water just travels straight through the blue top instead of through the filter.
And then when you re-attach it, you simply turn the top back to 'filter' and off you go.
You can use lots of types of filtration in it. I chose pleated paper cartridges at 50microns (so it catches the heavy stuff but doesn't interfere too much with the water flow), so nothing bigger than that gets through to the canister to muck it up with gunk now. You can go down to 10 microns to catch even the smallest gunk if you want.
So now I can just clean the the gunk out of this by-pass once a week and the canister can stay clean and working as a bio filter for ages (or so goes the theory). I've only had it for one week, but it's amazing how much muck it's already captured.
The water passes down the sides and then through the paper cartridge and flows back up the middle and out. It's a clear container, so you can see how dirty it is getting as the muck is caught on the outside of the cartridge. Very helpful to let you know when it needs to be cleaned.
For those interested, the filter cost was approx US $22, the paper cartridge is $9 (which is cleanable and re-usable).
PS. It comes with two 3/4 inch screw-in hose adaptors, but you can buy separate ones to match your own tubing system sizes exactly if you want.
PPS. You can also buy separate plastic internal containers to hold other type of filter media in it like charcoal for instance, so you can use it to filter anything you want! I guess you could even use it as a bio filter as well. Have three of them in a row (mech, bio & chem) with a strong pump and you probably wouldn't even need the canister filter!
