you'll likely find mulm build up on the biomax mesh bag. i normally just shake the bag off a bucket of water during a WC and replace into the filter.
Matrix is pretty much serves the same purpose as the biomax so it would be redundant. Adding more to top up the filter compartment wouldnt hurt as it increases the surface area for bacteria to grow.
only tip would be to clean only one of the medias at any given time, so if you were to clean out the foam sponge, leave the biomax alone, and vice versa. any cleaning would pertain to shaking loose debris from the media in tank water.
Matrix is pretty much serves the same purpose as the biomax so it would be redundant. Adding more to top up the filter compartment wouldnt hurt as it increases the surface area for bacteria to grow.
only tip would be to clean only one of the medias at any given time, so if you were to clean out the foam sponge, leave the biomax alone, and vice versa. any cleaning would pertain to shaking loose debris from the media in tank water.