I am not familiar with that brand but it appears that it is a cartridge style HOB
filter. Since you have two filters running what you might be able to do (space permitting) is take out the media from the old filter and replace it with a new cartridge. Next (of course after you have tested for sufficient space) cut the old media in half and place each half in the filters so that the current runs through the old media before running through the new media. This should help seed the new media.