Filter changeover

[bugdozer]

I have been running an air powered sponge filter in my tadpole/juvie tank since they were hatched in October. This has been fine so far but now the remaining residents are bigger and generating more waste, this little filter is struggling to keep the water good, and my nitrite readings have begun to creep up (ammonia seems OK though.) I've been keeping on top of it with water changes, but today I purchased an Aqua One HOB filter which should do a much more efficient job.
I seeded the filter by putting a little bit of sponge and a ceramic noodle with mulm all over it from my tropical fish tank into the new filter. I also still have the sponge filter running in the tank as well, as although it can't manage very well it is contributing at least a little and does have bacteria in it.
Does anyone know roughly how long I will need to run both filters together before I can take the sponge filter out entirely?

 

[auntiejude]

Can you take the sponge out of the old filter and put it in the new one? It should be possible with a cannister. In my experience it will take a few weeks to settle in anyway, it will just be smoother with the old medium in the new filter rather than run the 2 simultaneously.

 

[bugdozer]

No, it won't be possible to do that due to the different shape of the sponge and also the sponge filter is so fine that it won't permit the water flow through the new one at a fast enough rate - the filter would over flow.