Clean radiator, cool engine, coolant PH, flow, fans, shrouds.
Rice Nuker:
If you don't have the background or the materials to adjust the pH yourself, I would recommend using an off the shelf product like No-Rosion:
http://www.no-rosion.com/technical.htm
Use a 50/50 mix of distilled water & the coolant of your choice, then dose with No-Rosion.
One of the reasons I tell people to buy pre-mix for small jobs & make up after a repair is that the pre-mix is already buffered to the correct pH & hardness.
I just replaced a plastic / aluminum radiator that was 20 years old. It was the original unit in the vehicle, and failed about a year after a driveway flush & fill with local tap water / coolant. Calcium growth in the seam @ the gasket where the tank was crimped on literally bulged the aluminum header on the core.
B.