With regards to the FX5. Read a post about what a guy had done to improve his FX5.

If you want to increase bio capacity above that of the large Eheim range, remove the sponges and put in Alfagrog instead. Get a couple of sacks of it and brake it up into small pieces that could easily fit inside the outer compartments withour falling through the holes instead of the outer ring foam pieces. Gives you more than twice the bio however you do need an extra filter for mechanical filtration.

Water is clear, spotless and healthier than ever.

May I add that I removed the corrigated hoses as they are total S***T and add two plastic Y adapters that go from 1" to 5/8" switching from the normal pipe to two more clear flexible plastic lines about 6" from the filter. I now have
two 5/8" Eheim inlet pipes and two Eheim sparay bars running instead off of the FX5 hoses. I also got a small drill and widened the outlet holes on the spraybar slightly to improve the flow rate.

Have added a TetraTec EX1200 just for mechanical filtration so it has just sponges and change the floss once a week . I can use the top tray inside that for any other media I would like to add. Also got eheim inlet and outlet for my EX to match that of what I put on FX5. Everything looks neat and tidy and matches.

Based on my setup and amount of bio and mechanical filtration it is far better and cheaper than single 2080 ehiem. You also have two filters running if one should fail.

The FX5 is good but a few modifications make it far better.

What do you guys think. From what I can gather from spec of the FX5 you would end up with 30 Litres of bio and 4Litres of mechanical filtration from the Tetratec.

I have never used the FX5 although I was toying with the idea of getting one, either this or the professional three by Eheim, a real beast. Looks like he has really improved it by making it take more biological filtration. I use alfagrog in my sump filters so I know how good this stuff is. I think the FX5 is rated for 1200L, that's around 300 gallons, if your tank is a lot smaller than that, I don't think you need to go to the extent of having a completely separate filter for mechanical filtration,As long as you've got one fairly thick piece of sponge, that should be more than adequate. If you're finding that this size filter is clogging up very quickly, you should look at your cleaning and feeding regime.