Eheim Classic 2215 External filter
The Eheim Classic range of filters may seem old fashioned but bear with me a minute while i tell you why i'd recommend these classic filters. 1st there is no by-passing of filer media at all! this may seem like a trivial point as most manufacturers state that their filters have almost no by-passing of media because of some special device, but try placing a plastic bag across the bottom tray inside your external filter and see how it seems to filter as normal even though it should now be blocked! This will never happen with the classic range as the water enters in the bottom and exits thru the top, with no trays to pass around it has to go thru the media, thus 100% filtration guaranteed, no other filter does this not even Eheim's pro range.
The filter doesn't block very easily and although most modern filters need cleaning out once a fortnight this will go 6 months easy, sounds odd? well i've had one of these filters running on a heavily stocked tank for 5/6 years and it only been cleaned a dozen times max! If you think this sounds bad then you've got the wrong end of the stick, let me explain. Once the filter bacteria is established the only reason to clean the filter is to keep the flow going, a dirty filter does tend to get blocked thus killing the living bacteria inside the filter but with the Classic range you instantly know if it's blocked as the flow slows down, where-as most other externals will seem to be working ok even if the path to the media is blocked. Yes it gets dirty but what we see as dirt the bacteria see as an ideal living environment. They are also extremely quiet , i've had hagen, Rena XP 1 & XP 3, Eheim Ecco and Eheim professional External filters and they are all good in their own way but none touch the classic in terms of Quietness, length of time in between cleans, flow thru media and ease of use. Only draw back is the priming after cleaning is quite basic, needing you to suck on the flow pipe to get it started, but as this only needs doing once every 6 months on average it still wins on the cleaning stakes too.
The newer versions of the classic now comes with double taps for isolating the water from the flow pipes meaning the cleaning is now easier with zero mess and it's still the only filter that's silent, i have to either look at the flow thru the output pipe or touch the filter to see that it's still going. You won't get this with any other filter, the Rena XP is supposed to be silent but i've had an XP1 & an XP3 and both had very noticeable hums to them, the XP3 being the worse, i wouldn't recommend these for the lounge get an Eheim classic instead and you'll never hear it!!