MH Lighting question

[schippy]

I have a 55 reef. I have PC lighting. 2 10,000 and 2 actinic. I have tried to keep various corals but have not had much luck even with perfect water. They last for a while but eventually die. I believe it is due to the lights. I am thinking of upgradeing to a metal halide retrofit. The tank is a 55 so I need a 36 inch kit i think. They seem to hold ony one MH bulb in the middle and Either PC or VHO on the sides.
- Is one MH in the middle enough to evenly light the tank?
- Which kind of MH bulb is reccomended?
- should I get VHO or PC along with?
- How high above the tank do these light's need to be?
Thanks

 

[dskidmore]

What wattage is your PC fixture?
One MH fixture for every 2'x2' area is the standard recomendation, but if you prop the fixture up a bit higher, you can cover the whole 3' tank. There will be shome shading, the sides will not be as bright as the center. There is no real way to get around that with MH lighting, some people like the effect. Many people like to have thier MH bulb be a daylight/10000 Kelvin bulb, and suppliment with VHO actinics. The VHO will even out the light intensity in the tank and supply the extra blue light some corals like.
If you don't like the spotlight effect of MH, you could consider an additional PC ballast and adding to your existing PC lights. You could also go with 100% VHO, a slightly bulkier solution that gives a more even lighting throughout the tank.
I don't know about exact height. Several factors are in play. To reduce the spot effect or cool the temperature, you need to raise the lights. To get better intensity where your most light sensitive corals are, you'd want them closer to the water.