[Delphinus]

Blasting the corals with twice the intensity you had before, at full photoperiod, is a sure way to fry your corals. I'm sorry George, but I have to disagree with you on that one...

Even just a reduced photoperiod at full intensity is asking for trouble IMO.

The best way, IMO, is to reduce the intensity, either by raising the lights, or, by some other means. And then gradually ramp up the intensity over time until at 100% (i.e., lower the lights every day or two, until at the desired height.)

What I've also seen done in canopies where raising the lights or canopy wasn't an option, was a few layers of eggcrate. Four of five layers, and the guy removed one layer every 2-3 days.

I once had a halide bulb crack its casing (completely in two pieces). The piece at the end slid off about 1". It took me about 2 hours to notice that something was amiss in the tank. But the reason I did notice something was amiss was one of my acroporas, the one closest to the light, had completely fried. White as snow -- it was gone. Two hours. This is a slight apples to oranges comparison, but it goes to show that a sudden enough increase in UV is enough to kill corals, even corals that are generally regarded as "high-intensity-lighting required" corals ... ALWAYS go slow when changing things around.

If I were in your situation ... and I couldn't raise my lights and slowly lower them over time (which would be my first preference), and I also couldn't possibly go with eggcrate .... then my initial photoperiod on the second bulb would be no more than one hour for starters. I may be overly paranoid but I'm sorry if there's one thing I have learned is that it is exceptionally easy to go too fast in this hobby.

Good luck!