Hi Warr - no - if you want to conserve electricity you only have to have the metal halides on for a maximum period of 5 hours. I have read on some biological lab web-site, that the maximum period corals require for photosynthesis is 5:00 hours. Take into account that the sun is ONLY at it's strongest for just about this period in any normal in the tropics. The sun rising to it's highest point, and then setting again to it's lowest point, goes through certain gradients, and only from 45 degrees onwars to 90 degrees, on the y-axis, is when the corals actually have the possibility to photosynthesize - the sun's rays otherwise gets deflected off the water's surface too much, without having a real decent impact on the life below the surface.