What do you mean by recently?

Since the Winter?

You don't need additives in coolant unless you're trying to flush out gunk and you need a good solvent. Water is the best coolant there is-antifreeze is simply there to lower the freezing point and inhibit corrosion. Although antifreeze does raise the boiling point of water, it has a much lower specific heat capacity and heat of vaporisation than water and reduces cooling capability.