IMO

Ive run mag pumps for years and have not had any problems from heat do to using them, as well as countless other reefers. I sware by them.

The temp you keep your house and where you have the tank can influrence temps also. My house is always 74-75 year round which helps keep the tank temp stable. airflow over the surface of the water both of the aquarium and the sump is important.

Id buy a cheap clamp fan from walmart and attatch it in your stand to blow in the sump. ive done this on several aquariums and it helps alot. computer fans really do not move enough air to cool the water. i put my fans on a timers.

ive kept aquariums of all sizes over the last 10years+ and have never needed a chiller...