I don't have a chiller,and I run 250watt mhs, and 4 96 pcs on my 135gal. I have 2 cooling fans installed in the hood. My temp is steady between 79- 81 degrees. During the summer, when the lights are on, I blow a fan at the front of the tank and leave the canopy door a little opened. You probably would be fine without a chiller as long as you don't live in a warm climate, and have extra fans on the hot days.