you guys forget that they live to be like 50. he will be fine in that until he is around 4 inches or just until you notice him looking too big for the tank. i kept 2 painted turtles at a time in a 20 long with a turtle dock. i would catch one, keep it for a year or two then catch another and release my original. They do fine just being thrown back into the lake/river where you caught him.