Foams for outer parts of trays should be cut to 37.5cm (14.75") x 9cm (3.5"). You will be able to cut 3 foams from each 17" x 11" coarse and medium foam so as this kit has 1 set of foams that allows for 3 x half sections of outer foams with the strips of foam completing the foam section in last tray to ensure there is enough foams for both trays of the FX4.
The fine pads can be carefully ripped to a suitable thickness then cut to size for the top tray - you only need one fine pad on top of the top tray.
This video explains the full process of upgrading an FX6 and also applies to an FX5 / FX4:
HOW TO UPGRADE AN FX6 / FX5
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Reviewer: Jason Reading
Made an amazing difference to my tank. Water is clearer between weekly water changes. Less algae on the glass and fish are more active.
Would recommend for anyone with this filter unit as so much better than what you get in the box.