In my experience, Ocean Rider Mustangs and Sunbursts (Hippocampus erectus) do best at stable water temperatures in the range between 72°F-78°F, with 75°F being optimum. They may begin to experience heat stress and associated health problems when the water temperature approaches 80°F or above for any length of time.
In other words, Jelly, if your aquarium system typically runs between 78°F-81°F, it would be best if you can install a small aquarium chiller that can drop the water temperature in your tank. 3°F-5°F in order to avoid heat stress and subsequent health problems during those summertime heat waves.
Best wishes with all your fishes, Jelly!
Pete Giwojna, Ocean Rider Tech Support