Water flow is crucial to aquarium health. However, there is such thing as too much flow or the wrong type. These could lead to sand storms in the tank, as well as tissue damage among corals. The tissue damage will usually occur in areas of extremely high, laminar water flow, especially if the coral is in the direct path of flow. To decrease the chances of these negative events, I would recommend using multiple small water pumps instead of fewer larger ones. This will also help to remove or prevent dead spots, or areas of minimal water flow where detritus accumulates.