Sorry if my post sounded like babies needed cooler temps at night, all ages of veiled chameleons need those temps. 75 F day ambient temp, 85-90 degree basking temp, and 55-65 temp at night. You may want to consider just putting him in a different room if you can't get the temps to drop.
He will also need to have a barrier of some sort put up so he can't see the fish/water at all.