Water Quality

For the fish, it is important to keep the water in the aquarium as clean and balanced as possible. This requires an efficient filter system and the water must also be changed at regular intervals. Although you can keep many freshwater fish in water coming from the pipeline, you should know how to check the water quality and how to change the values if necessary.

Tap water
Water is treated for human use and contains certain chemicals everywhere. Some of these are poisonous for fish. For removal of heavy metals such as Copper or Zinc Water Conditioners can be used for water treatment and mostly they have other beneficial affects on the water, too.

Too acid or too basic?
When acids or bases are dissolved in water, these hydrogen ions dissipate and thereby change the pH value. The content of hydrogen ions determines whether the water is acidic or basic. In most aqueous solutions, the pH values ​​are between 0 (strongly acid) and 14 (strongly alkaline), 7 being a neutral value in the chemical sense. The pH scale is logarithmic and the jump from one pH unit to the next corresponds to a ten-fold increase in the acid or base concentration.

For almost all fish in freshwater aquariums, pH values ​​between 6.5 and 8.5 are well suited. Fish from black water rivers prefer soft water with pH values ​​between 6.0 and 7.5. East African cichlids like hard water with pH values ​​between 7.5 and 8.5 and high carbonate hardness.

If fish are subjected to a sudden change in the pH (e.g., by reaction), they are under stress. As a result, they do not absorb enough oxygen, their colors can fade, and thick mucus may form on the skin.

Too hard or too soft?
Water hardness is the concentration of the ions of the alkaline earth metals dissolved in the water (e.g., calcium or magnesium). The nearer fresh water is tapped at its natural source, the softer it will generally be. On its further path, it absorbs different amounts of minerals and becomes increasingly harder.

As with the pH value, the hardness can be determined by means of various test sets from the specialist trade. Up to a total hardness of 10 ° H, water is described as soft, between 10 and 20 ° H as medium hard and over 20 ° H as hard.

Fish have very different demands on water hardness. Some come from hard water, others from soft. Similar to pH, they do not tolerate any major fluctuations in water hardness without health problems. When it comes to the multiplication of the fish, one must usually soften the water. For this purpose, a reverse osmosis system or an ion exchanger can be used. Otherwise you should take a higher hardness simply as given and the selection of the fish according to it.

Nitrite Level

In case of insufficient biological purification, fish can suffer from poisoning by nitrogen compounds. These arrive e.g. By excretion of the fish into the water. Filters remove turbidity and absorb certain solutes, but with all organic waste they are not finished.

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The toxic ammonia is produced first, which can already have a damaging effect on sensitive fish with a content of 0.1 mg / l. Particularly critical for the fish is also the toxic nitrite. It is formed by the decomposition of ammonia or ammonium, by nitrosomonas bacteria. Intact filter systems achieve nitrite concentrations below 0.3 mg / l. In the longer term, a value of 0.8 mg / l should not be exceeded.

In the last stage of construction, nitrobacterial bacteria build up nitrite to the relatively safe nitrate. Plants take nitrate as a nutrient. Too high concentration, however, is harmful to ornamental fish and promotes the annoying algae growth. With a nitrate content of up to 25 mg / l, the aquarium water is still unproblematic; for values ​​above, an immediate partial water change is recommended.

How to change Water Parameters




PH Value

Lowering (acidulate)

  • Peat Filtration
  • Adding Co2
  • Water Supplements( e.g. xxxxxxxxxxxx)

PH Value

Increasing (basify)

  • Adding Sodium Carbonate
  • Expelling CO2 by aeration of the Water with air pump and air stone
  • Water Supplements( e.g. xxxxxxxxxxxx)



  • Demineralize the Water through Resins (Ion exchangers) or Reverse Osmosis Systems
  • Peat Filtration
  • Water Supplements( e.g. xxxxxxxxxxxx)



  • Slowly Adding Calcium- or Magnesium sulfate
  • Lime Filtration



  • partly Water Change
  • Cleaning Filter regularly
  • (fast) growing Plants
  • Water Conditioners (e.g xxxxxxxx)

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