One post per topic please.
Is your HPS air cooled?
You have to ventilate well to get rid of paint fumes before adding plants.
How long did you rung the HPS before taking temp measurements?
How tall are your waterfarm units? Are they actual Waterfarms that stand ~14" high? 4 feet headspace, minus a foot for the light, minus 14" for the buckets, minus the 18" you need between a HPS 400 and the canopy, leaves four inches for the plants.

Try a SOG on the floor of the box, using newly-rooted clones in 6" quart pots, the short style, not the tall deep ones.