The best thing you can do for the environment is not ot change the coolant frequently. Coolant typcially last 5-6 years or 100,000 miles.

People make too big of a deal out of coolant. Buy a name brand or from the Honda dealer... and be doen wiht it. Cooling systems are overbuilt by at least 30% so that he radiator can take significant damamge and the water pump and thermostat can begien ot wear without the system overheating.