I'll have to agree with the heat issue, I know its a hard one to control. Maybe get a couple of extra exhaust fans or a cooler of some kind. The symptoms also can indicate root problems, such as root aphids, or worse, root rot, a fungas that attacks the roots. To check for that gently remove the root mass from the pot ( easiest when soil is dry) and check the color of the roots. Are they a nice white color? Or are they brownish or tan looking?

If dealing with a root problem then a hyrogen peroxide flush will help. I use a 28% hydrogen peroxide that I got at the hydro store and use 5 ml. per gal of water and give it a good flushing. This will kill virtually everything in the soil, and supplies extra oxygen to the root zone. I've had plants come back from the dead doing this.

You have to get a handle on that heat issue though first thing. I had to purchas a small portable swamp cooler to cool my flower room down as I couldn't go with a air conditioner due to not having sufficiant electrical supply, which would have been better.

Check the roots and let us know.

Hope this helps