New Tank...

That depends on your plans for this tank and any other.

If it is to replace another tank, move the whole filter or just the media (cut any media up to make it fit) and decor and fish over at the same time.
If you will be running other tank(s) as well, take up to a third of the media from another filter and either add fish to the amount of a third of the fish in that other tank, then add new fish a few at a time; or add that third of the media from the other tank and do a fishless cycle, then stock fully.

Ah, that's a bit more complicated.

What you need are a few largish containers, and if they don't have lids you also need something to cover them eg old towels, bits of board etc. I have a 60 litre plastic dustbin with lid, a couple of those would be perfect.

For a few days before transfer day, feed the fish half rations. This will cut down on the amount of ammonia they make. On transfer day, don't feed them at all. For a few days after, feed half rations again.

Siphon as much water as you can into the containers, net the fish into the biggest one, put the filter and heater in there too and switch them on. Plants and other decor can go into another container of tank water, they'll be OK without a heater or filter. However, if you are using the built in Juwel filter you'll have to leave that behind and just float the media in the container.

Throw away the last water in the tank and move the old tank out. Move the new tank into position, add substrate and start filling with warmed water. If you have live plants, put them in at whatever stage that is usually done (sorry, I don't have plants growing in the substrate so I don't know when that is  ). Once you have put in enough water to leave enough room for what is in the containers, start putting the old water and decor into the new tank. Leave the container with the fish till last so they don't get too stressed. Move the heater and filter from the last container, and if there is enough water turn them on. If not, wait till there is enough before turning them on. Move the old water from the last container, netting the fish as you go.
Leave the lights off for the rest of the day.
If you will be using a different filter in the new tank, put the old one in the container with the fish but instead of moving the whole filter in the new tank, put all the media into the new filter and top up with new media. And if the new tank has a new heater, just turn that on when the water is deep enough.

Then go and sort out the old tank.


You will lose the bacteria on the substrate and the walls of the old tank. Check ammonia and nitrite daily, doing water changes if necessary. Once you have a week of double zeros, the tank will be fine.

Don't forget to add more fish a few at a time, testing the water for a few days after each addition.

Matt has reminded me about the substrate.

If it is one that needs a good bit of washing, do that before you start to empty the old tank. That way you don't have to stop half way to wash gravel/sand only to find it takes ages to do.