Im pretty sure its not heat.You can run into the 90s and not have to much stress.I like low to mid 80s.
I grow in soil myself but your leaves look like mine do when im root bound.
Look at the roots are they white?
If they are brownish they are not as healthy as the should be.
I know this is not much help so far But check the roots and let us know.Im sure people here can get you the info you need