I wonder how that generic matrix would hold up, and compare against seachems version? Anyways, 4 pages in, and no one brought up her ammonia readings?
Laticauda can i ask how big your tank is, how many fish, your water change %, and how often, and how long the tank has been setup for? If your tank has been running awhile simply upgrading biological media isnt the absolute solution here. Personally i'd use the pond matrix for the fx5, and the regular matrix in the HOB's. You need the bigger media in the fx5, especially with its high flow rate, but i see the regular smaller size like i use in your HOB's to be more beneficial as the flow rate, and smaller size will give the water a little more dwell time going in, and around the smaller version, and personally over all more surface area coverage then pond size.