I have come across a bunch of metal halide

[Jeff000]

Metal Halide what? Blubs? Ballasts? complete fixtures?
What bulbs? what ballasts? what voltage?

[Rogue951]

should be good. it's comes down to the bulb in it for spectrum. However 400 watts is a LOT of light. only people with deep tanks would be able to use them without frying most of their inhabitants.

[daplatapus]

Take a look on the bulb themselves and see if there's a temp rating on them. Eg. 10,000 K, 15,000K 20,000K