The RO membranes must be cleaned with high and low pH cleaning chemicals. High pH cleaning should always be done first to remove biological or organic impurities, which contain carboxylic functional groups. These weak acids gain an anionic charge at high pH, ​​allowing them to disperse. High pH cleaning chemicals remove calcium that binds impurities and biofilms with each other and with the membrane surface. Products like NaOH are only slightly effective due to their inability to remove the calcium bridge. The use of citric acid is recommended before high pH cleaning by some companies, due to its chelating properties. We strongly recommend against this practice - organic foulants lose their anionic charge if a low pH cleaning is done first.