The pH value of the water is one of the most important factors for all life forms in the water. Values in excess of pH 7 to 8.5 are ideal for garden ponds. During early mornings the values can also be slightly below and during evenings slightly above these ideal values.
The ph value is a measure of the strength of an acid or a base. It is indicated on a scale from 0‑ 14. Clean water is referred to as neutral with a pH value of 7; tap water usually has a pH value between 7.0 and 8.5. Alkaline solutions have a pH value greater than 7. The higher the pH value above 7, the more alkaline the solution. For example household soap solutions with pH values of approximately 10 are known. Acid solutions have a pH value less than 7. The lower the pH value below 7, the stronger the acid. For example, concentrated hydrochloric acid is a strong acid with a pH value below 1. However carbonated liquids, such as mineral water also have an acidic reaction. Optimal for a variety of life in the garden pond are pH values between pH 7 and pH 8.5. At measured values below pH 6 and above pH 9 the possibility of harm to skin and gills of the fish cannot be excluded, and in the extreme case these values can cause fish kill.
Chemically speaking water has the formula H2O. This means that there are two hydrogen atoms (H), and one oxygen atom (O) in each molecule of water. These water molecules break down into hydroxide ions with a negative charge (OH-) and hydrogen ions with a positive charge (H+). Thus in total the molecule remains neutral nonetheless.
The definition of the pH value was determined by the concentration of hydrogen ions. To avoid having to work with cumbersome numbers the pH value was defined as the negative logarithm of hydrogen ion concentration. At a hydrogen ion concentration of 0.01 mol/l (= 10-2 mol/l) for example, the solution in question has a pH value of 2.
The higher the concentration of hydrogen ions the lower the pH value. If the pH value drops from 7 to 6, then the concentration of hydrogen ions increases by a factor of 10.