The pH value is probably the most important and meaningful value that provides information about the quality of the water. It indicates whether the water is acidic or alkaline and whether there are good living conditions for fish and plants. We recommend pH values of between 7.5 and 8.5, as pH values outside of this range are unfavourable for organisms and should be avoided.
The conductivity of water reflects its salinity. Conductivity is measured in µs/cm (microsiemens per cm). Fresh water or pond water should have a conductivity of between 300 and 1200 µS/cm. If the conductivity is lower, even the most minor of influences may result in the water reacting with a significant change in the pH value, for example. Water begins to be considered as salt water from a conductivity value of greater than 1200 µS/cm.
The concentration of calcium hydrogen carbonate present in a body of water is of crucial importance for the pH value to remain stable. The carbonate hardness, also known as temporary hardness, is the measure of this concentration. A sufficiently high carbonate hardness in a body of water can stabilise the pH value of the water and successfully counteract a variation in the pH value. As with the total hardness, the carbonate hardness of a body of water is given in °d.H. or mmol/l and should be between 5 and 12°d.H. in natural fresh water.
In addition to dissolved gases, water also contains dissolved minerals (ions). The magnesium and calcium ions dissolved in the water play an important role — these are also referred to as hardness formers. The concentrations of magnesium and calcium ions dissolved in the water constitute the total hardness of the water. This is the sum of permanent and temporary hardness. The hardness of water is specified in the unit °d.H. or alternatively in mmol/l. Natural bodies of fresh water have a total hardness of between 5° and 20°d.H.
Nitrite is a nitrogen compound that can enter pond water by way of contaminated drains, rainwater or food residues. There should be no nitrite present in an intact pond ecosystem. Concentrations of nitrite as low as 0.2 mg/l can have very harmful effects in a pond in the long term and may poison fish stocks. Nitrite accumulates in the blood of fish and prevents oxygen uptake. The fish show signs of asphyxiation. The nitrite also interacts with the pH value: the lower the pH value, the more toxic the nitrite that is present.
Like nitrite, ammonium is a nitrogen compound that can enter the pond from the microbiological degradation of fish excrement, through fertilisers or even through surface water. The pH value is an important parameter to determine how toxic the ammonium content is for aquatic organisms. At high pH values, the harmless ammonium transforms into toxic ammonia.
Phosphate is the main nutrient for algae. Even the slightest increase in phosphate to more than 0.035 mg/l can trigger excessive algae growth. Phosphates are introduced to the water by fish feed or by adding water that is rich with phosphate. The phosphates are absorbed by the algae, which is why no phosphates can be detected in the water despite excessive algae growth. The issue with this is that phosphates are released back into the water when the algae dies off, which can then cause new algae growth.