CI WT No. 38 is the dual-inhibitor treatment for closed-loop hot water and chilled water systems where the operator wants both fast passivation and long-film stability in one drum. It combines sodium nitrite, which rapidly passivates ferrous metal surfaces, with sodium molybdate, which helps maintain a more durable protective film over time. That makes it a strong fit for closed hydronic loops where corrosion and mineral deposition quietly reduce flow, cut heat-transfer efficiency, and shorten the life of pumps, piping, and heat exchangers. Where No. 34 covers a wider range of systems including steam service, No. 38 is the closed-loop-only option that adds nitrite fast-passivation to the molybdate film — both mechanisms working together in systems that stay closed and recirculate. This product is not suitable for steam boilers, where different volatile treatments are required. Maintain sodium molybdate at 150–200 ppm and system pH between 10.0 and 11.0 to keep both inhibitors active and the protective film intact. Two inhibitors, one drum, closed loops only — and the film holds.