I recently converted to a
canister filter. I went with Rena XP2. It seemed easiest to maintain and had a very good reputation. I would use caution in buying used equipment. There are some great deals, but buy from a trusted source. I have purchased used equipment and been quite pleased, so I am not saying don't - just be a wise consumer.

Ask why they are selling it. You can often find manuals for filters on-line - That way you can see first hand what they do, what they need, how to maintain, etc. Sorry I don't have more info on your specific question -