If you're so worried, just get pre-mixed and be done with it. Otherwise, follow the directions on every jug, which is almost always 50/50 with distilled water. If you are going to only dump and fill, stick with dexcool, if you are going to flush with some distilled water between dump and fill, feel free to go with any coolant you want really (green, blue, etc). But why risk it unless you really know the specifics? So just stick with dexcool in my opinion.