1. THE EFFECT OF PH ON FISH AND FISH POND
pH (Hydrogen Potential) is chemically defined as the negative logarithm of the concentration
of Hydrogen ions in a solution. Water consists of two molecules of Hydrogen (H) combined to
one molecule of Oxygen (O). Small portion of water molecules dissociates and gives equal
numbers of hydroxyl groups (OH-) and hydrogen ions (H+). It is evident that only equal
numbers of OH- and H+ can exist in pure water. The negative logarithm of 10-7 is 7, therefore
distilled water has a pH of 7 which is called neutral, meaning that equal numbers of H+ and OH-
are present or, in other words there is no surplus of either ions or negative groups. If acid is
added in the water ("acid" is defined as a compound that releases H+ when dissolved in water)
then the H+ molecules will accumulate in the water. Any solution with a pH less than 7.0 is
called acidic. The lower the value the stronger the acidic character. Concentrated acids have a pH
of nearly 0. At that pH only H+ exist. Most freshwater ponds have a natural pH in the range of 6
to 8. When the pH of most aquatic systems falls below 6 and especially below 5 it may have
serious effect.
Here are some effects of increased acidity on aquatic systems:
As the pH approaches 5, non-desirable species of plankton and mosses may begin to
invade, and populations of fish such as smallmouth bass disappear. Below a pH of 5, fish
populations begin to disappear, the bottom is covered with undecayed material, and
mosses may dominate nearshore areas.
Below a pH of 4.5, the water is essentially devoid of fish. Aluminium ions (Al3+) attached
to minerals in nearby soil can be released into ponds, where they can kill many kinds of
fish by stimulating excessive mucus formation. This asphyxiates the fish by clogging
their gills.
It can also cause chronic stress that may not kill individual fish, but leads to lower body
weight and smaller size and makes fish less able to compete for food and habitat. The
most serious chronic effect of increased acidity in surface waters appears to be
interference with the fish’ reproductive cycle. Calcium levels in the female fish may be
lowered to the point where she cannot produce eggs or the eggs fail to pass from the
ovaries or if fertilized, the eggs and/or larvae develop abnormally.

2. Extreme pH can kill adult fish and invertebrate life directly and can also damage
developing juvenile fish.
It will strip a fish of its slime coat and high pH level ‘chaps’ the skin of fish because of its
alkalinity.
When the pH of freshwater becomes highly alkaline (e.g. 9.6), the effects on fish may include:
 death
 damage to outer surfaces like gills, eyes, and skin and an inability to dispose of metabolic
wastes.
 High pH may also increase the toxicity of other substances. For example, the toxicity of
ammonia is ten times more severe at a pH of 8 than it is at pH 7. It is directly toxic to
aquatic life when it appears in alkaline conditions. Low concentrations of ammonia are
generally permitted for discharge.