Hey everyone. Just thought I’d make this in case you got a fluval fx4 or even the fx5/6 and would like to maximize its space. Currently my fx4 has been running for well over 2 months with no issues. Love the filter. Here’s how it’s set up. For both trays, I use the white foams that come with it. The top tray, instead of just using the “pond foam” style foam, I use a thin, roughly 1/8th inch polishing pad on the bottom of the red tray on the top white tray. Then use a medium density foam, then the black foam that comes with it. It just barely fits in but does fit. In the section right under the red tray on the top white tray, i use the bio media that comes with the filter. Then in the red tray in the second white tray I use matrix as a secondary bio media. Then in the bottom tray I use for chemical media, which I use carbon in a bag. If you don’t need this you could easily just remove the red tray and fill the entire second white tray with bio media. Also, I put in fluval prefilter media, which is the ceramic pieces that look like ceramic rings but are a hexagon shape. Eheim mech also works. These go into the outer ring in the bottom of the case of the filter. I found that these collect a lot of junk before getting to the first foams. If you have an fx5/6, than the middle white tray can be filled with bio media to increase bio filtration. I hope some find this useful if you get a fluval fx filter. I can also add links to what I got, which everything can be found on amazon fairly cheaply.
