What refrigerant/coolant should I use in the water cooler connected to the Dynasty 280?

Miller coolant No. 043 810 (a 50/50 solution) is recommended, which protects equipment down to -37°F (-38°C) and prevents algae growth. Distilled or deionized water is also acceptable for temperatures above 32°F (0°C). Using a coolant other than those listed in the manual voids the warranty on any component in contact with the coolant, such as the pump and radiator. (Page 19)