Seeding new filter with current media

[twintanks]

I am shortly going to be setting up a new 5-foot (1.5m) 360 litre coldwater tank for my old goldfish and a few weather-loaches.
They will be moving from their 180 litre tank, and I plan to use some of the media from their Fluval 206 filter to seed the new, larger 406 Fluval.
Now, normally I would do a fishless cycle and get everything going properly and tested before putting fish into the tank. In this instance, I am wondering whether it is feasible (and safe) to move all the filter media across to the new one, get it up and running in the new tank and move the fish shortly afterwards (asap since they'll be in their old tank without a functioning filter for half an hour or so).
I do not intend to add extra fish to the community at this time, so it'll be the same fish "moving house", so to speak.
I'd be grateful for any problems with this idea to be highlighted. Otherwise I'll just do the standard fishless cycle as I've done before, following the details at Fishforums.

 

[Essjay]

Moving all the filter media into the new filter at the same time as the fish is fine - and moving the fish 30 mins later counts as being at the same time.

You will lose the bacteria on the surfaces in the tank, so moving as much decor over as possible is a good idea, but you can't move the bacteria on the tank walls etc. I would feed the fish lightly for a few days before and after the move, and monitor the ammonia and nitrite redings until you are sure they are staying at zero. If you do see either of them, they won't last long.

A couple of years ago this is what I did when I upgraded and never saw even a tiny blip in the readings.

 

[twintanks]

Thanks essjay, that sounds very workable. I'm not wanting to rush the move but thought it would be good to take advantage of having fully-functioning sponges, etc.

 

[Gruntle]

Yup. You should have most of your bacteria living in the filter (it's impossible to tell, they're very very small) but science suggests they should be living in a place with a good water flow (like a filter). Moving the media is the best way to move the majority of the bacteria colony.

The colonies should double in size (if necessary) within a day, based on their reproduction rates. So if anything you might see a momentary blip, but with a food source, the bacteria will multiply pretty quickly to process it.

Not feeding them for a couple of days before the move will reduce the load required to be processed (less food = less poop) and you should be right.