As the cold weather is appraoching in the northern hemisphere what
antifreeze can be used safely in integral water ballast tanks such as
in my Ventus? Also where do you buy it at a reasonable price?

I am guessing the maximum use would be about 25% v/v at any time. I
think I could often use 2gal Ethanol to 13gal of water in each wing.

Methanol
Ethanol
Isopropyl alcohol
Propylene glycol
Others?

Thanks,

Tim