pH value

The pH value indicates how acidic water is. Acidic water has a pH of below 7. Alkaline water has a pH of above 7. Understanding the pH of pond water is very important because it tells us something about the CO2 content of the water. Pond water typically has a pH well above 7. If we want to measure the pH value, we also need to know the KH value, the carbonate hardness. If both values are known, we can fairly accurately read the CO2 content per liter of water. At least 5 mg of CO2 per liter of pond water is required for good plant growth.

With normal carbonate hardness and sufficient CO2, the pH value of the pond water will be relatively low. At the same KH but insufficient CO2, the pH value will be relatively high. Now the CO2 level during a 24-hour period is not constant, but fluctuates under the influence of day and night, the so-called assimilation process. Underwater plants absorb CO2 and release oxygen with the help of light. The CO2 content decreases as the day progresses. At night, this process is reversed and plants take in oxygen and release CO2.

The action of microorganisms

Microorganisms, the largest producers of CO2, supply CO2 day and night. Due to these factors, CO2 will accumulate at night and decrease significantly in the afternoon. By the way, this process will only occur in well-functioning water bodies, that is, when there is a growing stock of underwater plants and sufficient activity of the microorganisms. With pH we can control this process. If early in the morning the pH is relatively low (pH 7 – 8) and measured in the evening relatively high (pH 8 – 9) then the pond environment is functioning, the plants will grow well and the water will be clear.

An excessive pH level (pH 9 to pH 10) need not be a problem, but is always the result of a poorly functioning pond environment. For example, it may be that the activity of microorganisms is nil. It may also be that biogenic decalcification is taking place in the environment due to excessive algae growth. In biogenic decalcification, calcium carbonate is insoluble in water and precipitates on the leaves of the plants. This process usually occurs in hard water with massive plant growth.

Measures to bring pH levels to favorable levels in the longer term should be based on activating the microorganisms (soil substrate and bacterial culture) and on introducing pond plants that do not rely on the water for their CO2 supply. Plants that are also in contact with the air such as floating plants, water lilies and marsh plants. The use of a peat granules can expedite the lowering of pH levels.

Acidification

The pH level does not normally fall below pH 7. However, if the GH level is too low, there is insufficient calcium to bind the excess CO2. The environment becomes acidic and oxygen deficiency occurs. The pH value in this case drops to values below pH 6.

A pH meter can be used to determine pH levels very precisely. Just as accurate and much more economical is a simple pH test.