Hercules® Refractometer

The answer depends on which Cryo-Tek antifreeze is being used, and what level of freeze protection is required. For more information, see this chart. Freeze point:  The temperature at which crystals begin to form. Pumpable:  The temperature at which there are sufficient crystals to impede the flow of the product. Burst protection:  The temperature at which pipes burst.  

Each strip has two pads.  One pad measures the level of propylene glycol, the other measures the level of corrosion inhibitor.  These levels should be checked as part of routine boiler maintenance.