I have an old (1990) WF unit that is about to be replaced with a new unit. They old system loop is pressurized and will now be non-pressurized loop with the Geo-Flo GeoPrime set up. Realizing there will likely be a need to add more fluid to the reservoir initially. My questions are: Is there a way to test the type of existing antifreeze in the system? To know what to add back. or Is there a "universal" antifreeze that could added to the existing fluid that is compatible with what might be in there? My existing fluid is slightly yellow(ish) clear fluid with no odor. It starts to get slushy at about 10 degrees. I live in Northern Arkansas. Thanks for your help.