The best way would be to figure out what is raising the temperature. If it is your lighting, use a fan to blow the heat away from the water surface. But it could be equipment such as powerheads or faulty heaters. On that note run your heater through a Ranco controller to make sure the thermostat on your heater isn't off (they are off frequently). But like Greenbean said, your temperature is not extreme yet. If you don't expect it to get much higher than that I wouldn't worry about it.