Upgraded MH on my frag tank, need help with light acclimation

[symbiodinium]

I have a 20L that I keep my frags in, 50% Millepora's, 20% Montipora, 15% Acans and 15% Zoa's.

I had a Coralife 150 DE MH with a Phoeniex 14K that I modded and replaced the PC's with T5's. I just purchased a Hamilton Cayman 250 DE MH 20K XM bulb with Lumatek ballast, how far off the water line should I place the light start to acclimate my corals?

 

[sirreal63]

As far as the MH, there is very little difference in a 150 watt Phoenix and a 250 watt XM 20k, the PAR is almost the same. The Cayman reflector is a vast improvement over the Coralife so it will do a better job of getting the light into the tank. I would start out with the bottom of the reflector at least a foot off the tank, if the corals start to bleach, move it higher or use some fiberglass window screen to help cut down the light.