So, unfortunately things aren't going well with my community tank. I'll be getting rid of my gourami shortly. I'm going to change to a goldfish tank, and I need a bigger filter. So, my question is, how do I go about changing the filter? Should I get the new filter, put the cartridge in the tank as it is and wait a little bit for the bacteria to colonize on the new cartridge? Or should I set up the new filter in the tank and put the old cartridge in the tank as if it were like a wannabe sponge filter and wait for it to colonize that way? I'm also keeping some of the old gravel to help colonize as well. :;dk WDYT?