Those ballasts can push HQI, 150, 175, and 250 watts. Could I possibly run them at 175? I had one set of magnetic ballasts in the past and hated the Heat, Hum, and all the extra space they needed. But I don't know. I still might go with the Aqua Medic 150.
http://www.marinedepot.com/Lumatek_250W