A dual pH suction cleaner system is more effective than just one. Bevisto W2 (pH 11.5) Bi-weekly is used with Bevisto W1. 1 ltr converts to 25x 2ltr treatments. No Phenols, No Aldehydes and non-foaming. Biodegradable to OECD standards. Comes free with a W1-W2 laminated calendar so the nurse can keep record of each treatment.