25 is too small. I have kept Rainbows and Angels, my favorite fish, for years in a 30, 55 and now a 75 gallon. The 30 didn’t work. 55 was good, but limit your number of Rainbows to three/four. They are constant fast moving fish. I can see the difference in growth and general happiness with the length and depth of the 75. I have ten in there, Different types (I go for color!!) no problems. Rainbows grow to striking colors!! (Can’t tell when they are small.). Have fun!!