EG=(Ethylene Glycol) and PG =(Propylene Glycol). EG is More toxic etc but the heat dissipation properties are better. EG is what 99% of dieses use, unless sometime has changed.
The hydrometer (Floating Ball Tester ) is the thing that has the balls in it. I think that is what it is called. You can also buy a Refractometer for getting very very close.
I used to use Distilled water but it is high in phosphates and other garbage. So I use Reverse Osmosis/ Deionization (RO/DI). It also from Total Dissolved Solids from the water. It removes 99.9% of all the junk in the water. Please do not think I bought this just for my tractors etc, I bought it for my salt water reef tank but I also use this water for my cars. It is the closest you can get to being “100% pure”. So less crap in water is less “things” to worry about with the coolant. Example, more junk in water makes your PH and others things move around to much. You will get less variance in chemical properties etc using better water.
…But then again, I take things to max at times.