Okay, so I'm big on "rinsing the same cartridge with old tank water and popping it back in the filter to maintain the cycle." However, the current one in my 29g is just getting ripped to shreds (bladder snails sometimes find their way in there and must just be biting at it). I slid a new cartridge in the reservoir with the media sponges to grow some bacteria. How long should I keep the slimy old cartridge in with the new one before taking it out? I was going to leave them in together for a week before making the swap, but should I wait longer? Thanks!