Chemtrol® CH250 Digital ORP/pH Controller with Sensor, 110V, 230V or 24 VAC Polystyrene Cabinet. Chemtrol® 250 is a microprocessor-based digital controller designed to maintain both sanitizer ORP (oxidation-reduction potential or Redox) and water pH in residential pools and spas, commercial pools and spas, hotels, motels, health clubs, apartments buildings, condo associations and industrial water treatment. Simplicity of installation, compatible with all common sanitizers and oxidizers, ease of use and long-term reliability.