The Puffer Forum

How long does it take a new filter to fill up with good bacteria if it's placed on an already cycled tank with another filter that is already full of good bacteria? Same time as a cycle would take? (a month or so)

6 weeks & it will contain <1/2 the bacteria to support the bioload of the tank.

So in about 12 weeks I can take the old filter off and just run the new one?

You can but keep an eye on the parameters, as you will be removing some of the good bacteria.

Why don't you split the bacteria filled media and put half in the old one and half in the new one

The filter that is already filled with bacteria is a completely different filter than the new one.

The old one is a Tetra Whisper that uses a bioscrubber http://www.tetra-fish.com/sites/TetraFi ... px?id=2416

And the new one is an AquaClear 50 which uses a biomax filter insert http://www.petfooddirect.com/product/15 ... ia-Insert-

It was a good idea Arny but as you can see they're two completely different media types.

Also do remember that if the bacteria are 1/2 in each of the two units, when separated to run independently, the remaining unit can double in 24 hours. That shoid be competent to handle the full load quickly. Just skip a day or two feeding and you should be home free with no detectable ammonia or nitrite.

HTH

Why not just keep both filters running? Extra filtration doesn't hurt anything.