Без рубрики

The water for aquarium

ūdens akvārijam

Water for aquarium is very specific topic that aquarists, with the help of different testing systems, often know better than the chemists. As nowadays the use of osmotic water for the aquarium are more often discussed, we decided to explore this topic a little bit more.

What kind of water is needed in the aquarium?

People who do not differ much from each other in terms of functional characteristic can drink water of the same composition, fish are more selective. There are fish that live in fresh water and fish that live in salty water- the composition of water for different species can vary a lot.

This is mainly due to the fact that the tissues of organisms living in water are adapted to maintain balance due to osmotic processes, just like the human body.  An ideal example would be intravenous administration of sodium chloride solutions. A salt solution containing 0.9% salt produces an osmotic pressure equal to the pressure in human blood. Pure water will cause the cell to swell but too concentrated solution will cause the cell to shrink due to dehydration.

For this reason different compositions of water are provided for different breeds of fish. The main and most difficult task for an aquarist is to maintain this composition stable, without sharp changes.

What kind of water is the best for an aquarium?

ūdens akvārijam

Important parameters that are standardized for aquarium water are: temperature, pH level, total and carbonate hardness, ammonium, nitrites, nitrates, phosphates and chlorine. The requirements for aquarium water are given by one of the sources. For each fish species they may differ a bit, but within the specified limit values.

Various fish

African cichlids Plants and freshwater fish Discus fish

Sea fish

Temperature, °C

24 – 27

23 – 27 24 – 27 28 – 30

24 – 27

pH level

7.0 – 7.8

8.0 – 9.0 6.5 – 7.4 6.5 – 7.0

7.8 – 8.4

Carbonate hardness, mg-eq/l

1,4 – 2,9

3,56 – 8,92 0,36 – 1,42 0,36 – 1,42

2,85 – 6,41

General hardness, mg-eq/l

1,4 – 3,6

5,4 – 8,9 1,07 – 2,14 1,07 – 2,14

3,57 – 7,13

Ammonium (NH;NH+), mg/l


Nitrites (NO), mg/l


Nitrates (NO), mg/l

< 50

< 50 < 30 < 10

< 30

Phosphates (PO4), mg/l

< 0.5

< 0.5 < 0.05 < 0.05

< 0.5

Chlorine, mg/l


The parameters for aquarium water

pH level

The pH level in the aquarium, as in any other liquid environment, shows whether the water is acidic or alkaline. The neutral pH level is 7, if it is lower, the environment will be acidic, if it is higher, the environment will be alkaline. This parameter is measured very often since it tends to fluctuate due to the small volume of water. A decrease in pH level is usually observed as a result of fish feces, rotting algae and uneaten food but carbonated rocks at the bottom of the tank are responsible for the increase in pH level.

Experienced aquarists advise compensating the system by adding pebbles, such as calcite, to the bottom to neutralize the acidity. Sometimes it is leveled by adding source water with a neutral pH.

Total hardness

Total hardness determines the amount of dissolved salts of alkaline earth metals (mainly calcium and magnesium) which bind to various anions (mainly chlorides, sulfates, bicarbonates).

Carbonate hardness

Carbonate hardness is the part of hardness salts (hydrocarbonates) that is removed by boiling. These components are biogenic and necessary for the full development of fish. At the same time too hard water in the aquarium can be dangerous for many freshwater creatures.

Ammonium, nitrites and nitrates

Ammonium, nitrites and nitrates are interconnected. Ammonia is released with the waste products of fish and its accumulation in water can be dangerous. In order to avoid the harmful effects of ammonia, bacteria need to break it down first into the still dangerous nitrites and only then into the usual nitrates. Ammonium and nitrites are very dangerous for fish, as well as for all living creatures, so it is important not to overclean the aquarium filter, where colonies of beneficial bacteria like to live. As for nitrates, they are the safest in the nitrogen cycle, but their concentration also plays a serious role.

It is important to remember the fact that the MPC of nitrates in tap water is 50 mg/l and the actual content is usually in the range of 20-50 mg/l. In spring and well water the nitrate content can reach even higher values, so the control of the parameter is very important.


Phosphates enter aquariums either through bacteria or through tap water. They are not dangerous for fish but they provoke active reproduction of algae, both –that are planted in the aquarium and that are unwanted ones that cover the walls and filter of the aquarium. For this reason it is recommended to control phosphate level in aquarium water.


Chlorine, which is added to water for disinfection, is dangerous for fish and algae. As a result of oxidation, it can cause damage to the tissues of fish and algae as well as slow down the vital activity of bacteria, leading to a violation of the nitrogen cycle.

The sources for aquarium water

There are several sources of water for an aquarium: tap, spring, rain and filtered water.

Tap water for aquariums is the most commonly used because access to it is unlimited. Tap water’s main disadvantage is possible pollution with chlorine, nitrates, phosphates, increased water hardness. But in general the tap water is suitable for ordinary fish. The main thing is to check the parameters and, if necessary, dilute the water with distillate or with water from a reverse osmosis filter.

As for spring water, it requires careful analysis. Its composition is less predictable: multiple levels of nitrates, phosphates and pesticides are possible. If you decide to use spring or well water, you should have a full set of testers and carefully monitor water’s composition.

However, the rainwater can be really clean, but due to the fact that it collects all the contents of the atmosphere, it must be collected in ecologically safe regions and only a few minutes after the start of rain. It is important to remember that rainwater must not be collected from asbestos and rusty metal roofs.

Aquarium and the water filters

The water for aquarium

There are two types of filters that may be suitable for an aquarium:

  1. triple filter;
  2. reverse osmosis filter.

Triple filters are three flasks installed in series, which contain:

  • activated carbon to remove chlorine and organic matter;
  • ion exchange resins to remove hardness salts, heavy metals, etc.

The only drawback is the fact that during the ion exchange process calcium and magnesium are exchanged for sodium, which can be bad for freshwater fish.

Is reverse osmosis suitable for an aquarium?

Reverse osmosis ensures that all impurities are removed, making the water “too clean” even for freshwater fish. Experienced aquarists use reverse osmosis water as a base for preparing an optimal environment for a variety of fish, both marine and freshwater. Osmosis water can also be used to dilute water in an aquarium.

Back to list

Related Posts

Leave a Reply

Your email address will not be published. Required fields are marked *