top of page
parametres ideaux

Explanation of the parameters


Organic waste is transformed into ammonia (NH3) which is very dangerous for fish and ammonium (NH4) which is not very toxic. Ammonia is transformed into nitrites (NO2-) thanks to a nitrifying bacteria called Nitrosomonas . It is important to regularly check the concentration of nitrites, because even in low concentrations, it affects the red blood cells of aquatic animals, reducing their capacity to carry oxygen and thus causing suffocation and death of the fish or axolotl. Ideally, the nitrite level in the aquarium is zero.

The nitrites are then degraded into nitrates (NO3-) by the action of the Nitrobacter bacterium. Nitrates can turn back into nitrites [if your changes in au are not made regularly to lower nitrates (No3)], nitric oxide, nitrogen oxide and then nitrogen gas (N2). This information tells us that we must actively monitor the presence of nitrites (NO2-) in the aquarium otherwise all life in it will die quickly . It is also important not to overfeed the fish and to regularly clean the bottom of the aquarium: this eliminates the main source of organic waste. The nitrogen cycle also teaches us that it is important to change part of the water regularly because if bacteria make it possible to recycle organic waste, the non-renewed water in an aquarium inevitably sees its nitrate level rise. . In addition, the bacteria we discussed above are not naturally present in water, so there must be an external supply of these bacteria.

Urgency to lower nitrites, but only if there is no other solution because it is always better to avoid any addition in the aquarium, and let nature work. Nitrit-minus


The main causes of too high nitrate levels

The nitrate level must remain below 20 mg / liter. Beyond that, it becomes dangerous for axolotls and fish. If the nitrate level exceeds 25 mg, here are some possible causes:

- Excess of food

- Overpopulation of the tank (never exceed 1 cm of fish per liter, this is only valid for small fish. A large fish such as the discus or the scalar needs 50 liter on its own

) - Poor maintenance of the tank: water changes not frequent enough, leaves of dead plants left in the tank, filter too dirty or in poor condition ...

- Water changes with water loaded with nitrates (rare). Plants play a role in regulating nitrate levels, since they consume them to grow. It is therefore important to plant well, when the tank and the housed population allow it. If your pipe water is loaded with nitrates, resins are sold to lower this rate, they should be incorporated into the filter media. The totally natural ones have been listed for you here .

In addition to this, you will need to know more about it.

Here are the main water parameters to know in aquariums. There are still many others such as Po4 phosphates (toxic), iron (necessary for plants). The important thing is to respect the needs of the fish, to maintain the tank regularly and not to play petty chemists: no need to buy so-called “miracle” products which are supposed to modify the parameters (pH, nitrates.). They can be dangerous and completely disrupt the balance. Regular tests verify the quality of the water. In strips or drops, there are all kinds. Drop tests, although more expensive, are the most accurate. (see below)

Water quality in France new UFC QUE CHOISIR card:


Green : Low Hardness, GH <9
Orange : Medium Hardness, GH> 9 <15
Yellow : Strong Hardness, GH> 15 <20
Blue : Very High Hardness, GH> 20

In addition to this, you will need to know more about it.

Ideal values for our axolotls


In short !


GH in detail

The total hardness, GH (or TH in French degree but never used TH = 1.78 × 1 ° GH): it corresponds to the calcium and magnesium salts contained in the water and results from the accumulation of the carbonate hardness and the permanent hardness. The richer the water is in calcium and magnesium salts, the harder and therefore calcareous (commonly) it is.

A GH hardness of 5 ° to 10 ° corresponds to soft water. Some tests are displayed in German degrees, the tests giving this value. To convert TH into GH, multiply the TH value by 0.56 Carbonate hardness (KH in German degree or TAC in French degree): these are the carbonates and bicarbonates of calcium and magnesium which disappear after boiling water . They are therefore temporary. KH acts as a buffer on the pH. Permanent hardness: these are the calcium sulphates and chlorides which remain present after boiling. The pH: it corresponds to the degree of acidity of the water. Below 7 the pH is acidic, above 7 it is basic, equal to 7, it is neutral. The pH varies during the day: at night it decreases because the plants reject CO2, during the day it rises because the plants consume the CO2 for photosynthesis. The most important parameter to take into account for the welfare of the fish is the total hardness. It is necessary to respect the requirements of the fish with regard to this parameter. The pH must also be respected, especially for very delicate species such as the Discus for example. Axolotls need hard water that is either hard (GH = 10 to 15) and basic (pH> 7). Below 10 for the GH we are in soft water, that is to say going towards acidity. However, the minerality of water is essential for the proper functioning of the axolotl organism and especially of its digestive system. Above 20 we are on a very dangerous GH on the other hand, be vigilant. Recurrent yeast infection is often caused by inappropriate or abruptly changed GH.

The natural evaporation of water from an aquarium causes the remaining water to become harder and harder, a hardness that must be corrected by partial water replacements.

Adjust GH and KH

Each aquatic species has specific requirements when it comes to water quality. Unsuitable water is synonymous with difficult or even compromised survival. The article does not separate GH and KH because, very often, voluntarily or involuntarily, the modifications intervene on the 2 parameters. GH or hardness corresponds to the amount of calcium and magnesium ions. Ca2 + and Mg2 +. GH gives a vague idea of ​​the minerality of water (other ions). The KH or carbonate hardness, corresponds to the quantity of hydrogen carbonate ions (also called bicarbonates). HCO3-. The KH corresponds to the role of buffering power by preventing the pH from moving. This is why before being able to modify the pH of a water, it is necessary to lower its KH, ie its resistance to variations in pH. These two parameters play an essential role and generally the two parameters go hand in hand: - some fish like hard and basic waters, this is particularly the case of fish from African lakes. It may then be necessary to increase the GH and the KH some fish like fresh and acidic water, this is particularly the case of Amazonian fish including discus.

In addition to this, you will need to know more about it.

Water suitable for a population is a guarantee of good health and survival of living beings in the aquarium.

In addition to this, you will need to know more about it.

Means influencing GH:

  • on the rise: limestone, Preis salts , CaCO3, MgCO3, CaSO4, MgSO4, Ca2Cl, Mg2Cl

  • downwards: reverse osmosis water, rain water, Montroucous water

Means influencing the KH:

  • on the rise: limestone, CaCO3, MgCO3

  • downwards: reverse osmosis water, rain water, Montroucous water

In short !

I have pipe water that is too hard, how do I lower the pH and the hardness of the water?

Most tap water is hard and has a basic pH, so reverse osmosis water should be used as a supplement if you want to reduce hardness and pH. Just buy it in aquarist store and mix it with tap water. This balances the temperatures between the water purchased, that of the tap and that of the tank. It is not recommended to pour the reverse osmosis water directly into the tank, its very low pH and its almost zero hardness could cause a shock for the axolotls. The carbonate hardness must also not be less than 4, otherwise the pH will be unstable. In fact, KH acts as a buffer on the pH. It will therefore be useless to try to lower the pH of a water if the KH is too high: it will not work. Lowering KH leads to lower pH. Adding CO2 or filtering through peat can also be used to lower the pH, but again, if the water has high hardness (GH and KH), the CO2 and peat will have no effect. It could even be harmful.

Conductivity (EC or Electrical Conductivity) measures the ability of water to conduct electric current. All the ions in the water participate in it: calcium, magnesium, but also aluminum, iron, manganese, mercury, potassium, lead, sodium, etc.


Conductivity at 25 ° C (µS / cm) Estimated TH - Water hardness

<300 <17 Fresh water

Between 300 and 550 Between 17 and 30 Hard water

Between 550 and 950 Between 30 and 55 Very hard water

> 950> 55 Extremely hard water


The different water tests

There are 2 types of tests: strip tests, which come in the form of small strips of paper that will take on different colors depending on the settings. They are not very precise and only give an indication of the result. Besides, often totally wrong concerning No2 and No3.

It is therefore necessary to prefer
tests in drops . Their use is simple: take water from the aquarium then add the number of drops of reagents indicated. The water will then take on a color that must be compared to a color chart. These tests are much more reliable and precise, therefore to be preferred even if their cost is higher. The JBL brand being the most reliable of all. (no I have no shares with them ^^).

For the pH, it is important to do the light off test as explained above: at night the plants reject CO2 and the pH is therefore lower. During the day, plants consume CO2 and therefore the pH increases ...

Tests must be carried out regularly, especially nitrites and nitrates, to ensure that everything is going for the best!

I always prefer to measure in GH and KH (German units) because to my knowledge it is only in France that we see these two units change. The rest of the world (when browsing the web pages) expresses everything in German unity.
So a measure in German advice will prevent you from converting but in case you want to stay on French units here is a summary.

(The GH is a German unit for expressing total hardness.
The dH is a French unit to express the total hardness.
And yes suddenly many get lost there and rightly so!
KH is a German unit for expressing carbonate hardness.
dH or th is a French unit to express carbonate hardness.
To convert from German to French, enter GHx1.78 = dGH
Ditto for KHx1.78 = dH)

Click on the images to be directed to the merchant sites

To harden GH

JBL Test Case

Unit tests

Warning : the use of these tests must remain reasonable (once a week at most). It is necessary to avoid making any decision based on these tests alone because generally these tests lead beginners to carry out brutal and destabilizing actions for the baccalaureate. You have to learn to observe living things.

Details :
- below a KH of 3, the pH of the aquarium can fluctuate easily and weaken the fish. In the case of low KH, provision should be made to stabilize the pH by an appropriate means.

- plants need carbon to thrive. They usually use CO2 from fish respiration or from CO2 injection. In the event that the quantities of CO2 become insufficient, the plants will look for the carbon atom present in the hydrogen carbonate ion HCO3- responsible for KH. This results in a drop in KH which can become dangerous. This is particularly the case with powerful lighting combined with very insufficient changes or the absence of CO2 injection.

RO water: better to be interested in GH
Let us take the case of water at 10 ° KH and 10 ° GH. By using 60% reverse osmosis water during the changes, we obtain a KH of 4 but we also lower the GH to 4.
Adding reverse osmosis water lowers KH AND GH. However, if certain species like fresh water (low PH) they have difficulty withstanding too low a hardness (GH). They need the various mineral salts provided by the mains water, including calcium (one of the components of GH).
It is therefore necessary to take an interest in GH when considering the use of reverse osmosis water.

Be careful when buying your axolotls (or fish), you must be able to provide them with the appropriate parameters. The modification of the water parameters is often imposed on the aquarist.
These manipulations do not pose any problem with the means available. Especially since most species have fairly wide tolerance ranges, so it is often unnecessary to adjust the parameters to the nearest degree GH or KH.

Reduce nitrites in an emergency, especially not in the context of an aquarium prowl: Nitrit-minus


Can be used during major water changes. Denitrol

Calculate the GH of mineral or spring water?

GH = Calcium rate in mg per Liter / 7.1338 + Magnesium rate in mg per Liter / 4.3254

Example with this bottle of Evian

GH = Calcium rate in mg per Liter / 7.1338 + Magnesium rate in mg per Liter / 4.3254
GH = 78 / 7.1338 + 24 / 4.3254
GH = 10.9338 + 5.5486
GH = 16.48

bottom of page