I'm about to swap my original filter in my 300l tank for a new external filter. My tank is fully stocked and I don't want to lose any fish because of this change. How can I change over to the new filter (different size, shape, brand) without losing the "good" bacteria in the tank.

Thanks!

Well I'm new to aquariums so I could be wrong but so far from what I've heard I think the answer is: run both filters for a week or two. That will give the new filter time to grow new bacteria, then you just take the old filter off. Someone else may have a better idea but I think this would work.

That'll work. If you can't do that, shove the old media in with the new media into the new filter. If that won't work, I saw someone shove their old gravel (filter for you) into a leg stocking and leave that sitting in the bottom of the tank.

Point being, find some way to continuing using the old media alongside the new media.

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100 Dirt + Stuff. To be Angel baby tank.
37 Planted. http://www.aquariumforum.com/f45/pla...nal-20774.html
29 Tall community tank. 5+ Years up and running.
15 Soon to be RCS tank.

I am new to aquariums but I read a really good idea that worked for me...I was to change the filer sponge, so, to make sure that the good bacteria colonize in the new sponge, I cut a couple of cubes (about 2 square inch each) out from my old sponge and kept one on top of the new sponge and another below it. That worked for me, since I have not seen a rise in Ammonia or Nitrite levels! Hope this helps!