Metal Halide height?

Hi everyone, I picked up some el cheapo ex supermarket metal halide lights
at a flea market with the external ballast thingies and was wondering what
the general consensus is as to height placement above the cover-glass. I've
only got a 4300K in it atm and will upgrade the light fitting to over 6500K
pref 10000K when I find an affordable outlet. Can these lights give fish
cataracts or other eye problems ie when surface feeding they have to look
up?