I do not believe it was/is co2 causing the yellow. Removing plants from the room you learned what? I would have looked at the roots, if they were healthy I would try some different foliar sprays.
I just got back up, my apprentice quit after getting spider mites on one plant,this after he had scales, pm, root aphids, then the mites. I left him to his ways knowing he was going to owe me in the end,some people just do not want to accept help. Figuring they can grow as good as this old fool.
Anyways I have some plants in veg that looks like yours. I thought he had RA again because it looks like a mag dif. I cut one container open,then cut the root ball in half. No unhealthy roots or bugs. Sprayed the last two days with dif nutrients on dif branches too early to tell. No co2. If I just saw a pic I would have guessed cold roots, but being in socal right now that just is not the problem here.
I will post back here if I discover the problem. Also bought him a new batch of nutes in case there was a bad batch,not that that has ever happened before. JK