I realize that this is PondBoss, and we strive for accuracy and live and die by what the manual says, but is it possible that we're overcomplicating and overthinking this situation?
Alcohol is flammable, can attack rubber and plastic components, provides no lubricating qualities, and in some formulations can be toxic.
Propylene Glycol based RV antifreeze contains no alcohol, is not harmful to rubber or plastic lines or seals, has lubrication qualities, and is non-toxic. it's used in the rv and MARINE industry to treat potable water systems, as well as engine cooling systems in order to provide freeze protection.
My experience with it in a campground situation has seen literally gallons of it flushed from the water systems of RV's and campers over the years, a great deal of which went right into these ponds I now own. We never saw that first problem. And while Nate and Justin are new campground owners, after touring their operation this past winter I am pretty confident that the same procedure has taken place there over the years, albeit on a much larger scale.
And, propylene glycol based RV antifreeze is inexpensive and readily available. It is recommended that you purchase virgin propylene glycol however, as some is reclaimed from the airline industry where it is commonly used as deicing fluid.
