Units of measurement for water hardness
There are different units of measurement for water hardness. The hardness range is mostly used by municipal utilities and detergent manufacturers. In aquaristics, the water hardness is usually given in degrees of German water hardness (°d). Soft or hard water is often simply spoken of. The following table is therefore intended to provide guidelines for classifying the various units of measurement.
below 3° d (0) very soft water below 7° d 1 soft water below 14° d 2 medium hard water below 21° d 3 hard water above 21° d 4 very hard water
When using the table, it must be taken into account that this information cannot be an absolute value in aquaristics. For a fish from extremely soft water, even water with 6° d can be hard.
In the literature, there are sometimes somewhat different assessments of the degrees of hardness, e.g. B. includes hard water. However, the table above allows the simplest and at the same time unambiguous assignment of the three essential units of measurement.
Why the water hardness in aquarium water can be lower than in tap water without water treatment
Various processes in the aquarium can remove hardening substances from the aquarium, even if no peat or other targeted softening methods are used.
- Calcium can be precipitated as phosphate by overfeeding.
- Many fast-growing snails can take so much calcium from the water to build their shells that there is no longer any calcium in the water if calcium is not replenished by regular water changes. Examples are apple snails, Helisoma and Radix ovata.
- phosphate-containing agents, e.g. B. to lower the pH value, can reduce the water hardness.
- Fast-growing aquatic plants such as tomentosum, Vallisneria and waterweed absorb hardeners.
- The water hardness can decrease through biogenic decalcification of the plants.
- Acids are formed during nitrification, which lower the water hardness if little water is changed.
- In aquariums with a pH lower than 7, the water hardness will decrease over time if only a few water changes are made.
A slight change in water hardness through these natural processes is harmless. In aquariums that have not yet been established, it can make sense to aim for slightly higher hardness values or to prevent the hardness from being reduced so that the pH value does not become too low or remains stable. Because the bacterial cultures are not yet working properly, there can be strong fluctuations in the water values due to the biochemical processes, e.g. B. overfeeding. But these are rare exceptions.
Process to reduce water hardness
- Slight subsidence is possible with peat.
- A strong reduction is possible with an osmosis system.
- A strong reduction is possible with an ion exchanger.
With an osmosis system or an ion exchanger in connection with hardening salts or by mixing it with tap water, practically any water hardness can be adjusted. At the same time, an osmosis system lowers high nitrate and phosphate levels and reduces other pollutants. Another advantage is that the water remains the same even after a move and there are no problems due to changed water.
A demineralizer must be used as the ion exchanger. Desalinators exchange OH- for H+ ions. Full desalinators must be regenerated regularly with hydrochloric acid (HCl) or caustic soda (NaOH). On the other hand, the water consumption is much lower than with osmosis systems because there is no residual water. Any desired water hardness can also be set with demineralizers by adding softening salts or mixing it with tap water.
Water from osmosis systems and demineralizers should not be used in the long term without using softening salts or without mixing it with tap water. Otherwise, the consequences are a lack of trace elements and extremely low water hardness. If the tap water is unsuitable because e.g. If, for example, there is a lot of nitrate in the water, the use of hardening salts remains.
Neutral exchangers that are regenerated with salt are not suitable. Basically, neutral exchangers do not remove the hardness, but replace cations with sodium and chlorine. The hardness is exchanged for Na+ and CL- ions or hardness is exchanged for common salt. This exchange shifts the ion spectrum of the water and makes it unsuitable for aquaristics. In some fish species, the change in the ion spectrum leads to problems in osmosis regulation.
The water will be soft, but not low in salt. The conductivity remains high and there is a lot of table salt in the water. The water is therefore not suitable for soft-water fish. Partial desalination can be useful under certain conditions.
Ion exchangers contaminate very quickly. Because only freshly regenerated ion exchangers are low in germs, they have to be regenerated very often. This is not permitted for ion exchangers used in the production of food. These exchangers therefore contain silver as a disinfectant. These include e.g. B. the Brita water filter. Silver kills the germs.
The water softened in this way also contains traces of silver. This silver attacks the filter bacteria as well as unwanted germs. Because the silver is deposited in the soil, the microfauna that are important and desired in the aquarium, e.g. B. bacteria in the filter and substrate, damaged over time more and more.
Such filters are therefore unsuitable for aquaristics.
A good alternative to water treatment, especially for beginners, is to only keep fish for which the available tap water is suitable. Water or municipal utilities provide information about the most important water parameters free of charge.
Table salt does not change the water hardness.
When salt is usually spoken of, table salt is meant. Table salt is sodium chloride.
However, the water hardness only refers to the calcium and magnesium ions. Table salt contains neither calcium nor magnesium. Table salt therefore does not harden the water and has no influence on the water hardness.
However, adding salt to water increases the conductivity of the water. The conductivity is the sum of all ions in the water.
In the case of soft-water fish, an increase in conductivity should be avoided.
Salt is added to prevent external parasites. Because this puts a lot of stress on the osmosis regulation, i.e. the maintenance of a certain osmotic pressure in the cells, of the soft-water fish, salt should not be added as a preventive measure. Soft water fish are adapted to very low salinity levels and have major problems at higher salinity levels. But there are fish that have a very wide range of adaptation, e.g. B. Rainbow fish and many seasonal killifish. Salt should only be added in case of illness and then better as an external bath. Of course, brackish water fish also need salt.