The harder the water is, the
the water is more alkaline.
The softer the water is, the more acidic the water is. This relationship is valid for most waters. Since the term water hardness is not used clearly in aquaristics, misinterpretations can occur.
Water hardness can mean in aquaristics
- the carbonate hardness (KH)
- the total hardness (GH)
- a high salt content
When talking about hard water, e.g. B. salty water can be meant, but its carbonate hardness is low and its pH can be in the acidic range.
The greater the total hardness, the
more calcium and magnesium salts are present in the water.
Total hardness measures the amount of calcium and magnesium in the water, as these are the main hardeners. Calcium plays an important role in the metabolism of fish and plants. There are other salts in the water, but these are not measured in the total hardness, such as sodium and potassium. Water can therefore be more salty than the total hardness indicates.
The content of all salts in the water is determined with a conductivity meter. The salt content provides information on whether the water is suitable for soft-water fish. Soft water is always low in salt in the original areas of origin of the fish. In parts of Central Europe, such as the Rhein-Main area, the water is often high in sodium, chloride and sulphate. In these areas, the total hardness cannot be used to determine the salinity of the water. In areas with water without much additional salt, such as the tap water in Munich, the salt content can be estimated relatively well from the total hardness.
Carbonate hardness is created by the combination of calcium and magnesium with carbon dioxide. These compounds are called bicarbonates or carbonates. The carbonate hardness indicates the content of calcium hydrogen carbonate. The higher the hardness, the more carbon dioxide can be bound. Therefore, it is better to speak of the acid-binding capacity or the acid-binding capacity (SBV). In aquaristics, however, the term carbonate hardness has become commonplace. Part of the carbon dioxide is converted into carbonic acid in the water. Since carbon dioxide is one of the main acids in aquarium water, the carbonic acid in the water has a significant impact on the pH value of the water. The higher the carbonate hardness, the more carbon dioxide is bound.
With the same total amount of carbon dioxide, there is less carbonic acid dissolved in the water with higher carbonate hardness. This means that the pH value is also higher.
The more carbon dioxide (CO2) in the water, the
the pH is lower.
The pH value measures how acidic or basic the water is. Carbon dioxide essentially determines the acidity in aquariums. The more carbon dioxide there is in the water, the more carbonic acid is dissolved in the water and acidifies the water.
Doubling the CO2 content lowers the pH value by around 0.3 units while the carbonate hardness remains the same. This is independent of the level of carbonate hardness and the initial value of the CO2 value.
Halving the carbonate hardness also lowers the pH value by around 0.3 units while the CO2 content remains the same, since the lower the carbonate hardness, the less carbon dioxide is bound and more carbonic acid is dissolved in the water. Again, the initial values are irrelevant.
Do fish prefer slightly acidic water?
Slightly acidic water always has a correspondingly low carbonate hardness, so the water is soft in this respect. However, lowering the carbonate hardness of hard water is not enough to create water that softwater fish thrive in.
How is pH changed?
The pH value by itself does not play a particularly important role for the fish. If the salt content in the water changes, the pH value automatically drops. If there is still enough CO2 available to the plants, the pH value remains stable. In addition to slightly acidic water, soft-water fish need low carbonate hardness, low overall hardness and a low salt content. All four values are reduced with an osmosis system, a deionizer or distilled water.
Do many plants also consume a lot of CO2?
The CO2 consumption of the plants depends on the assimilation of the plants. Additional plants use more CO2. Fast-growing plants use more CO2 than slow-growing plants. Plants grow faster the stronger they are illuminated.
Where do plants get the CO2 they need during the break-in period without fish?
The CO2 required by plants is mainly produced by bacteria that process plant and feed residues. In some aquariums, the amount of CO2 generated in this way is sufficient; in other aquariums, additional CO2 must be introduced through CO2 fertilization.
Does the pH drop because fish excrete ammonia?
Organic substances, e.g. B. fish food, fish droppings and dead plant leaves contain nitrogen. At certain pH values, the nitrogen is converted into ammonia by bacteria. In the further course of the nitrogen cycle, nitrite and nitric acid (nitrate) are formed. The acid reacts with the calcium hydrogen carbonate, i.e. the carbonate hardness, to form CO2 and water. This reaction reduces the carbonate hardness and an acid drop is possible.
Plant growth can counteract the drop in acidity. Plants release calcium hydrogen carbonate when they absorb nutrients.