is 9 1/2 quarts which calls for 9 1/2 ounces of the RP Ice. If you've put a 12 oz bottle in your radiator you have 26.3% too much RPI in (12/9.5). If you remove 26.3% of the coolant/RPI mix and replace it with your normal coolant (50/50 water/antifreeze e.g.) you'll be back to the recommended RPI concentration. With 32 ounces per quart, 26.3% of 9.5 quarts = 80 ounces (9.5 x 32 x .263). Make sure the RPI is thoroughly mixed into your coolant before draining the 80 ounces.
Seems logical to me but I'm no chemist. Maybe someone else can verify the soundness of this suggestion.