Acid treatments for biological clogging problems

Adding acid (e.g., sulfuric acid, phosphoric acid, etc.) to water that has a biological contamination problem may help control the problem simply by making conditions inhospitable for the growth of biological contaminants.  The control of biological growth with acid, when pH adjustment is not needed for other reasons, is likely to be an expensive way to deal with the biological problem.  

Adding acid (and thereby lowering the water's pH) will have the benefit of making chlorine that is injected as a biocide more effective.  Adding chlorine to water produces mainly hypochlorous acid and hypochlorite.  Hypochlorous acid is the more effective biocide and its concentration depends on the water pH.  Note that the hypochlorous acid percentage increases from around 20% to over 80% as water pH drops from 8 to 7.

Acid and chorine should never be mixed together in the same tank since hazardous chlorine gas will be produced.  If you are going to inject both chlorine and acid, do so from separate tanks and at separate injection points.