Transitioning to larger tank

[GhostLincoln]

Hi all, I currently have a 20g tall and would like to upgrade to a 40g breeder in the next few months. Unfortunately I don’t really have the space to have both tanks set up simultaneously. Ideally I’d like to run the 40g for a few weeks with live plants to get it cycled. 
 

My plan is to reuse as much of the filter media, substrate, and plants as possible in the new setup. What else can I do to minimize the risk of ammonia spikes and other non-seasoned tank issues? Thanks! 

[JettsPapa]

Assuming the 20 gallon tall tank is well established, you should be able to move everything, including the fish, over to the new tank immediately.  Of course you should still monitor the tank for a while, and add new fish slowly, but the beneficial bacteria colony should be just fine as long as everything is kept wet while you're breaking down the 20 and moving the 40 into place.

The 40 gallon breeder is a great size, by the way.  It has a good sized footprint, which helps with stocking options, and it's not so tall that it's difficult to work in.

[Anon]

You can also go slow on the feeding to minimize risk of spikes, but like the other post says, you should be fine. I've moved fish into a new tank with seeded filters twice now and didn't have any spikes. 

[lefty o]

i agree with just swap them over. tear down the 20, put fish in 1 bucket, plants in a bowl, and substrate in a bucket. drain tank and remove. set up new tank adding in substrate, plants, decor, fill with proper temp water, add fish. your plants,substrate etc already have good bacteria, so when moving them all over, all the bacteria go with them. just dont add a pile of new fish on day 1 of the new tank.

[jwcarlson]

Just plop them in a bucket or tote and set up the new one.  If you don't think you can get it done in a reasonable amount of time you could refill the 20 even just "on the floor" if you think you need a day or two.  But if you move the filters over and dechlorinate the water you don't really have much to worry about.