I use the Tetratec EX700 external filter and I swear by it, any external filter I'm sure is as good or better and I find the Tetratec is so easy to maintain. Every Month I change the fine white filter, and every 6 months I either change the other rough filter sponges or just clean them out. They say to change them every 6 months but I know I can get years out of one sponge. Sure afterall they are there just for mechanical filtration anyway! The bioballs that hold the bacteria can be kept indefinately since they are solid plastic...Its a great unit to buy!
