I have just purchased a new Eheim Aquaball 130 to replace my (still functioning)Interpet PF2.
What is the best way to introduce the new filter to the tank? Should I just run both filters side by side for a couple of weeks or would I be better off putting the filter pads from the Interpet into the Eheim temporarily to allow the bacteria to cultivate?
Put the pads and the ceramic media into the new filter. Much of the bacteria will be on the little ceramic noodles in the sealed box, and you don't want to lose them. After a few weeks you can gradually remove the media the PF2 had from the Eheim, and replace it with new Eheim stuff. Or just leave it in there.