Definition of pH

• Natural waterways maintain their own pH balance.Jupiterimages/BananaStock/Getty Images
  
  Chemically, pH is a measurement of the concentration of hydrogen atoms in a solution. An acid solution has a pH of 0, and an alkaline solution has a pH of 14. A pH of 7 is considered neutral. While they may do well within a limited pH range, most fish kept as pets can't survive extreme fluctuations in the pH level of the water. Also, some species require a more specific pH to spawn than others.