I noticed that about the isolation tank, too. Having owned many aquariums with real fish in my time, you should always isolate the fish for medical treatment anyway. It would just make it more realistic to treat them in the isolation tank.

You do know that you can move your baby and teen fish into the for sale tank if you need more room but can't buy the second tank yet. They can't be sold until they are full grown, so you don't have to worry about that.