So 2 days ago my plants were fine growing great I come in today and all the tops are yellow and one plants dead sorry for poor quality pics I only have my phones camera
Looks like heat stress to me but could be any number of issues with nutes and/or pH. Tell us more about your grow environment - light type and distance from plants, size of grow pod, heat levels during lights-on, time since switching to 12-12, soil type & watering frequency, nutrients used, and the pH of your run-off after watering. Armed with that info, someone should be able to make a good run at it for you.
Did you have a recent break-up or rift with your sig/other? I ask because this is not overnight damage due to over or under attention. I went out of town 2 weeks ago and left my cloner pump unplugged. Lost 4, coulda saved 4. But at what price?
My brother was the one in the grow room the other day he said it was fine but now that I think about it, its been extremely hot for a while that would make sense