You could take the media from whichever filter you are running, and add it to the Eheim. The filter case is just that, a case that holds the media, allowing water to flow through it. The container doesn't cycle, the media does.
THe Ecco line is more of an entry level designed for smaller tanks. Less powerful pump, less media capacity, but it does have a couple of convenience features such as media baskets & a self prime.
The 2213, 15, and 17 are the traditional standard Eheim canisters. No self prime, no media baskets, but one great pump. These are probably the best bang for your buck, if you can do without the media baskets & self prime.
The pros have media baskets, but no self prime. Same great pump.
The pro IIs have the self prime, media baskets, flow adjustment, with a flow indicator. Plenty of bells & whistles, you want a light under your stand to display your filter as well as your tank with one of these.
So far I have a 2232, 2222, 2224, 2026, & 2215. Just picked up the 2215 at an auction over the weekend, $10, like new, with media & doube shutoffs. It even came with the manual.
