I run 2 x FX5s on my 350 and 1 x FX5 on my 150. I really think two on a 150 is overkill...particulalry, in terms of turbulence within the tank...but, that's me. I would install a single FX5 on the 150 and keep the other one for a reserve (if already purchased). Anyway, I use the white sponges provided and fill each central chamber with Ehfisubstrat Pro and my water quality is perfect. However, I also perform water changes religiously. Since the impeller is BELOW the media on an FX5 and depending upon the particular biomedia type (shape, diameter, etc.), you may want to install some fiberglass screen cutouts in the bottom of each media chamber to prevent fragments from falling through. I would recommend avoiding the use of any pads within the central media chambers.