If you have a piece of glass covering your tank then you just figured out your problem.
Remove the glass and replace with some eggcrate (if you are worried about jumping fish). Your pH likely will thank you as well! (Better 02 exchange)
Your fish likely would rather the tank be cooler, but shouldnt start dropping dead yet either although corals might start if it gets any warmer. Id suspect a negative impact on the fish soon if it gets any warmer.
Sounds like you have a greenhouse effect going on...