Nut burn is what it looks like to me. Are you using the fully recommended dose of Flora series? Also, a fan in the room to strengthen the stalks are a good idea to. I would clip the brown dead tips only. Don't pull the leaf, just clip off the dried part. This will prevent the dryness from spreading. How often are you watering them? With 90 degree room, they will need more water to recover from the dehydration the heat may be causing. What's your ppm level? Also, ph? Whatever they may be, your plants look pretty healthy. You need to get your nut level down, or water more often to compensate for the heat. Another possibility is that your plants were not receiving all the (N) and other nuts they needed before and your Flora Series will provide. I dilute all of my Grow, Bloom, and Micro. Are you adding your micro and bloom bossters first? This can be a problem. The micro must be put in the water first.

Good growing