Small and deep for its size. Does the kasco you have pull from the bottom or the top? Issue is typically going to be that the water on the top will, for the most part, have enough oxygen. Driving the circulation and breaking the stratification will be your challenge, so with that in mind, I would put 1 where it's the deepest and 3-5 around at the average depth areas. You could get away with just 3 total, IMHO.
