It is always best with two flow pumps but may not be necessary on newly set up reefs with minimal coral growth. I would suggest the XF230 placed horizontally near the surface on one of the short sides on your 4ft long tank. Then as your corals grow and the needs for more random flow throughout our reef, all you have to get is one 230 pump itself. It will plug right into your existing controller with one power supply. The XF250 requires a min of a 5ft tank to take advantage of the flow patterns but really works well with 6-8ft long tanks.