Last 2 years when the temps dropped into sub zero, the geo shut down...LWT looked to be about 24.5 at the time. I know there should have been more from a make up heat source but I was in the south and my backup plan failed. At any rate, what should the antifreeze solution be good to? I did a freezer test and at 24 degrees the "water" is thickening...20 no slush but heavy...18 light slush...14 heavy slush. The system uses glycol. Any thoughts on this?