I just set up a 6 bulb T5 fixture over my 75. It is a dimmable fixture. At 100% I had to raise the lights over 2.5 ft above the tank. Also with a window screen. The par levels were super high. Like 250 at the bottom. So be careful You don't burn anything. So now at 2 feet above , the fixture at 70% , the par readings are around 120 at the bottom.