Do fish tolerate water that is too soft or too hard better?
There is often a desire to socialize fish species that place different demands on water hardness, e.g. B. the popular combination of red tetras with viviparous fish such as guppies and platies. Red neons need soft water, guppies and platies need harder water. This raises the question of whether fish can be kept in softer or harder water than is actually recommended, and which of the two variants the fish tolerate better.
The clear answer
The clear answer is that fish should only be cared for in the recommended water conditions. Fish with different requirements should not be socialized.
The reasoning
Due to the osmosis regulation of the fish, softer or harder water always leads to a changed osmotic pressure and a changed supply of ions in the water. The affected fish has to coordinate three different influencing factors in order to keep the ion ratios in the body stable.
Influencing factors:
- Protection against too much water entering the body through the skin.
- Uptake of ions via gills and intestines.
- Excretion of water and ions through the kidneys.
StockSnap / Pixabay
The skin of soft water fishing is adapted to allow relatively little water to enter the body even though the osmotic pressure on the body is relatively high. Because few ions get into the body, soft-water fish absorb ions from food and water very effectively. At the same time, water is transported out of the body very effectively, since large amounts of water penetrate the body despite the adaptation. The elimination of ions is kept as low as possible. Despite these difficult conditions, the important ion ratios in the body remain stable due to the coordination of the three influencing factors.
If these soft-water fish live in water that is too hard, less water than usual gets into the body. This water, on the other hand, contains a larger amount of ions. So the fish has to adapt to taking in fewer ions from the same amount of food and water, otherwise too many ions will be taken in overall. The effect is similar to a human drinking salt water.
If fish live in softer water than usual, much more water penetrates into the body than usual because the skin does not offer the appropriate protection. However, the kidneys are not adapted to excreting large amounts of water and losing as few ions as possible. On the other hand, the gills and intestines are not designed to absorb ions from food and water as effectively as possible.
In both cases, the kidneys in particular are put under greater strain than usual in order to keep the required ions and water content within the necessary limits and balances. In both situations, the metabolism and especially the osmosis regulation must work differently from the usual stress. Such deviations cause stress, which leads to increased susceptibility to disease. The greater the deviations in water hardness from the usual values, the greater this stress and thus the vulnerability.
In addition, there are usually even stronger changes in pH that affect ion and water regulation. Higher levels of salt in the feed, high CO2 values with a high oxygen content in the water and similar things also affect osmosis regulation. All of these factors together ultimately lead to the increased stress leading to the onset of disease.
In African cichlids, water that is too acidic, e.g. B. lead to wounds that look like burns.
The bursting of cherries after a downpour is often cited as proof that water that is too soft is more harmful than water that is too hard because of the osmotic pressure. However, this comparison does not apply. The skin of cherries is covered with wax and is completely waterproof. So there is no osmosis, but the water is actively transported into the cherry.