Soldato
Depends how good the chiller is really.
With only -5c water temps your safe with just water as the flow will make sure it doesnt freeze, to -30c'ish you need to test different levels of water/antifreeze to see what gives better temps/viscocity.
Much below that and your looking into specialist stuff such as propylene glycol.
Then you also need to take into account its sensitivity (probably not the best word to use) to the temps, propylene glycol for example can pull down temps to maximum coldness quickish whereas pure denatured alcohol would take much longer to get to similar temp levels
With only -5c water temps your safe with just water as the flow will make sure it doesnt freeze, to -30c'ish you need to test different levels of water/antifreeze to see what gives better temps/viscocity.
Much below that and your looking into specialist stuff such as propylene glycol.
Then you also need to take into account its sensitivity (probably not the best word to use) to the temps, propylene glycol for example can pull down temps to maximum coldness quickish whereas pure denatured alcohol would take much longer to get to similar temp levels