I would increase the day temperature to 85 and keep the night temp at 75 degrees. In nature it is not unusual to see Red Eyed Tree Frogs BASKING--yes basking--in the sun. Sick frogs seek warmer temperatures (inducing a "fever") which triggers the frogs natural immune response. To induce fever, raise tank temperature to 90-95 degrees for eight hours, carefully monitoring your frog for stress. Give him the next day off, reducing the tank temperature to 85 degrees and repeat the fever on the third day, again, monitoring the frog to ensure he is tolerating the fever. Give him the 4th day off fever and induce fever again on the 5th day. Then maintain the 85 degree day temp and 75 degree night temp, and see how he does. Good luck.