Yeah I was gonna say it might just be light stress...goes from 400w to like what not even 200w of Fluro power, which we all know fluros dont really help too well and dont pound out lumens at all.
If you wanted to sustain a mother plant, my opinion is that you should have started the plant under fluros, then put it in the closet with fluros...not start it out with a 400w HPS. There just isnt enough light in the fluros compared to the 400w, on top of that heat from the HPS.
My 2 cents....