Can you fit BOTH in there?
I don't know what to tell ya.
On one hand, MH400 has greater light penetration than any flouro.
On the other hand, with correct bulbs (red spectrum), your T5 fixture is a better LIGHT for flowering, but won't penetrate deep into those somewhat tall plants.
Choosing one or the other, I'd go T5 and get it down RIGHT ON TOP of the plants, about 2-3" from the canopy, which you should actually try to tie over just a bit flatter if you are going to use flouros so that all parts are equally close.

Also, have you checked the pH of your soil runoff recently? That set of symptoms says to me "pH out of range plus overwatering plus possible cold soil". Are your pots sitting on a cold cellar floor, or do you have low night temps?