PR-25 additive was specially formulated to return the recycled coolant byproduct back to it's original state (after being mixed with water). It infuses corrosion inhibitors and protects internal components of the coolant system, including solder, aluminum, and other metal components within the system. Also will not harm plastics and hoses or other non metallic components. Preparol 25 also restores proper alkalinity and helps prevent overheating and prevents build-up. You will typically use one gallong for everyy 25 gallon batch of recycled end product. Sold in case of 4 one gallon jugs.