Couldn't you find a smaller tent?...this is gonna be tricky...:glugglug:

A 400 would burn things up...IMO. Even a 250 watt is iffy. It's the height, of the tent, that is the killer. And 2x2 is good for 2? plants.

Also...do you have 250 watt HPS magnetic ballast?...(digital ballasts don't work with CMH bulbs).