I have a SPS only tank. When I first saw these lights at WWC I fell in love. I was looking for something to replace my Chinese black boxes. so I pulled the trigger. My tank has offset overflows. the overflows prevented light from reaching the corners and they went dark. If I raised the lights to the 10 inches recommended by Kessil I reached the whole tank but I would need to raise my whole top layer of sps to make up for the loss of PAR from raising the light. I need 500 at my top layer for my light hungry sps. Kessil recommends 5 to 7 inches for sps which was giving great PAR numbers, but my corners were dark. I am placing my Chinese black boxes back on until I can sell this and get new lights. I have a 72''L X 18''w X 30''T 150 Gallon offset overflow. When I get a house and get a 300 gallon these are the light I will be getting again they are awsome.