I have this one on my 20g. Great little filter, but after a inline UV filter, it lacks a little flow that I need for my 20g long.20 Gallon I'd get the eheim 2213 it maxes out at 65 gallons.
i do not feel safe to buy any electronic item from ebay. Most of them say " NO return". What's happen if you have leaking filter or broken filter?Had both brands over the years and cant go wrong either way. I just won a bid on eBay today for a new Fluval 306 for $79 New in the box. Check out eBay. With a 20 gallon you could even roll with a Fluval 106.
Another great filter is the Rena Filstar XP S. That could work for you too. The Fistar is ultra quiet and easy maintenance.
Good luck
sold by :amazon.comEheim does not sell filters on amazon, or to anyone directly. They're a manufacturer that deals exclusively with distributors. I'd suggest contacting the distributor directly. Click on the little link in amazon that says sold by. That will take you to the distributor who sold you the product. But Eheims are far superior to fluval even though I'm also a huge fan of Hagen (fluval) I think eheim makes better filters. Fluval tries to patent their own parts and hoses that can only be used with their products, making it a pain to want to rhetro fit because you have to buy their overpriced parts.