I am getting an IM 200 ext penn. Wondeirng if i could do 3 xr30 or if i need to do 6 xr 15. The tank is 71 x 30 and 21 deep. i plan to keep any aquascaping atleast 5 inches form glass on all sides. Going to do a cavey negative space aquascape. Havent decided on what corals, but i dont want to be limited because of my light choice.