My 18 foot CC has a 19 gallon tank that sits on the stern of the boat. I completely drain and clean the tank thoroughly each spring, use 89 octane gas and put in plenty of additives. Nonetheless, if the boat is not regularly used I've experienced water/gas separation after 3 months. As a snow bird in Florida, you can get ethanol free 89 octane gas in many gas stations. In Anne Arundel county I can get 100 octane aviation fuel at Lee Airport. Would this high octane damage my 70hp fuel injected Suzuki outboard? I guess I could use a half and half mix to cut down on the octane level. Any help and information would be greatly appreciated.