I thought I would pipe up on this. If you have a fish that is going to be held for an extended time in a tank that is other wise empty of other fish, you may want to consider what I was taught. The tank by its nature has no fish in it, so it is not established. So what I do is take the water from the gravel vacuuming and put it in the tank, I will also put plants that were in an established tank (java ferns) in the holding tank. It has an under gravel and a bio wheel filter. This way the fish in question will not have to contend with the stresses in a tank that is not fully cycled. Just my 2 cents worth.