Re: What does the pH level do to a solution?

Water molecules are composed of 2 atoms of hydrogen (H) and 1 atom of 
Oxygen (O).  It is commonly written as H2O or HOH.  However, water and most 
other liquids really exist in the form of positive and negative ions.  In 
the case of water H+ and OH-.  pH is a measure of this hydrogen ion 
concentration in a solution.  The higher the H+ concentration (or lower the 
pH) the more acidic a solution.  As the H+ concentration is lowered (as the 
pH goes up) the solution becomes more basis or alkaline. (EX: Vinegar would 
be a mildly acidic solution and bleach would be a highly basic solution.) 

The pH scale goes from 1-14, with 1 being highly acidic and 14 being highly 
basic.  A pH of 7.0 would be considered neutral or not acidic or basic.  
Almost all living organisms and microorganisms live best in solutions close 
to this neutral pH (7.0).  Their internal machinery or enzyme systems tend 
to operate best at these neutral conditions.

If you add an acid to water you will lower the pH and the addition of a 
base such as bleach will raise the pH.  As a solution moves away from 
neutrality, pH 7.0, changes occur in the internal operation of the cells 
and eventually the cell machinery will shutdown, the cells will rupture and 
die.  

The solutions you are adding can also have other effects unrelated to 
pH that may cause direct toxicity to the microorganisms.  These toxic 
effects could directly shutdown cell functions leading to death.  therfore, 
your solutions could have multiple effects on the microorganisms.

Additional information on the effects of pH on microorganisms should be 
found in basis Environmental Sciences or Environmental Microbiology texts 
in your local Library.