if it is a 6' tank which i am assuming because you are looking at 80w bulbs i have heard that the 6' bulbs really start to loose there kick at the ends when they get that long something to research 6 bulbs across the top would be good for what you want i dont remember what the retros that long come in 4 or 6 bulb sets but if the one you want comes in 4 bulb sets than put 8 not 4 and remember most people find themselves getting into more light demanding coral as they progress in the hobby so more is always better in lighting when it comes to reef tsanks