HELP NEEDED URGNT - first grow :/

Let me just start off by saying the past two weeks haven’t been the kindest to the girls but I’ve been doing my best. Between an impromptu move, a tragic spell of sickness (Not COVID related thank God) and being a beginner I’m a little lost here.

Four autos in coco/perlite/cocoloco mix. 240w KB with another on the way. I water with purified water, Cal Mag and Trinity from RootsOrganic were my onlynutes until this week when I introduced mega rip, bud explosion and terpinator. My main problem is Pineapple Express, my runt. It’s obviously dying but I really don’t know why. Also, it looked just like the other plants 24 hours ago. Any ideas?