Par 38's may not be very cost effective up front for your size tank. I think eastamhearstbias has some par38's over a frag tank he may be able to add some insight. I can say that somewhere on RC I read a thread on choosing how many leds for x- amount of gallons for which array of corals, my 120 came to like 78 leds for the full range and I decided to go with 84 to have a little extra power and I can always dim them a bit. I will try to find that thread for you. I will be starting the official build thread probably within a week.