My veiltail killed one of my cories, but I am not punishing the VT for that. We know that their nature is a bit territorial so we should house them accorndingly. Individually or in large community tanks. I would have tohught though that the 55G tank would be enough so each fish could carve out his own niche. Bad luck I guess.
But a 1 gallon tank is fine, probided he does not need heating. Putting in a 1 gallon is okay. Putting him in a 1g and putting warm water that will eventualyl get cold, and replacing it with warm water will just stress and kill the fish.
The new water should be the same temp as the old water.