Originally Posted by Elpez
So how soon can I put my 5 gallon fish into the new tank after treating the water with prime?
Should I also use most of the 5 gallon tank water in the new tank? Or just the rocks will do?
Prime (and all other dechlorinators) work pretty much instantaneously, so the water will be dechlorinated within just a few moments.
You can move the water if you choose, but beneficial bacteria generally don't reside in the water but rather adhere themselves to the substrate, decorations, filter media, etc..
The rocks as well as any plants, decorations, or substrate will help as there will likely be some bacteria on them, but if your 5 gallon is cycled, moving the filter media (or the whole filter) over to the larger tank will give your new tank the biggest jump-start in terms of cycling. You can run it concurrently with whatever filter you have planned for the larger tank and it will slowly seed the larger filter with bacteria, while still providing filtration itself.
If you can, I'd run them concurrently for about a month, but then, your new filter should be fairly well seeded. Of course, you can run them concurrently indefinitely if you choose.