Help!! What's wrong with my plant??

Here is my Fruity Chronic Juice Plant! She is 3 weeks into flower. I'm growing her in a 3 gallon pot, using Pro-Mix BX as a medium and I've been using the Fox Farms nutrients! Grow Big, Big Bloom, and Tiger Bloom. I've been following the nutrient schedule to a T. This problem literally happened overnight. I use 600 watt HPS lights. My grow room stays at a consistent 80? Degrees at 50-55% humidity. Can anybody tell me what's wrong? Here are the pics of the plant, also it is the only one doing it out of 8 plants

Was she overwatered at one time recently? It got to hot ontop of an over watering me thinks. The leaves get weak and fragile when overwatered...then they cant take the heat ...fry up..like this

looks like nute burn but as the op said only 1 out of 8 is doing this so we need to trouble shoot. check the run off on this plant for ph, I would guess its to low...If it is below 5.8 I would flush this plant's root system immediately and let the soil or medium dry out a bit before you water again(3 days). Also what damage you see on the plant is also much the same in the roots so the plant needs time to heal... might take a week or so to see any improvement but it will snap back but wont yield much

sounds like you maybe a little on the generous side when it comes to watering... I wait until the pot is light and the top soil is dry and the soil has pulled away from sides of the pot.