If you already have the gear for a tank, then stick with the tank unless it totally bombs and you can't get anything right. I have my new rescue pastel in a 10 gallon and it took a few days but his temps and humidity are spot on perfect now. The main thing to remember with tanks is COVER. Cover the back and sides with solid dark background and insulation to keep heat in and cover the screen top 3/4 with foil and duct tape. In the Colorado winter, I've also taken to wrapping a thick towel or blanket around the back and sides as well (taking care not to block air flow for the UTH of course). Just give it the good try, and if after insulating and cover you still can't get things right, then go with a tub.