Abstract: A method and apparatus for chemical cleaning microfiltration and ultrafiltration membranes immersed in a tank involves backwashing a chemical cleaner through the membranes while the tank is empty of tank water. A backwash pump which drives the chemical cleaner is controlled by a speed controller which is in turn connected to a programmable logic control and, preferably pressure and flow indicators. The backwash pump is operated to supply the chemical cleaner to the membranes in pulses. The pressure of the pulses is high enough to reduce the relative size of pressure differentials between membranes or portions of membranes in varying places in the tank. The duration and frequency of the pulses is chosen to provide an appropriate contact time of the chemical, preferably without allowing the membranes to dry between pulses and without using excessive amounts of chemical.