I would add a few more powerheads myself. Knowing the number and types of powerheads is one aspect but another is how they are placed and how your tank is aquascaped.
Water will flow around your rock in a unique way and you really need to just analize how the water is flowing in and around your tank and then position the existing PH
's or get new PH
's to enhance areas of low flow or areas of near stagnant conditions.
I like to have areas in my tank that can be classified as high flow, medium flow and low flow. Remember what we dont want is a jet stream of current. Instead we want random currents that will sway the corals back and forth.
As an example of the kind of flow I have. On a 75 gal
tank I have 2 802 powerheads and a Mag 7 pump returning water from my sump. The 802's alternate on/off every 10minutes.