What is the hardness of water?
Rather than talking about what the hardness of water is, we should refer to what it measures the hardness of water.
Water hardness measures the content of dissolved calcium and magnesium salts in the water.
Thus, we can affirm that hard water has a high concentration of mineral salts, while soft water has a low amount of calcium and magnesium salts in its composition.
How is the hardness of water measured?
There are two ways to measure water hardness, in French TH degrees or German DH degrees .
Typically, we find that most tests use German DH grades, equivalent to the amount of lime contained in the water. They are measured in milligrams of dissolved salts per liter of water.
Some tests express the results in ppm or parts per million, which we can interpret as milligrams per liter mg / l.
Test and Kits to measure water quality
In the market we will find all kinds of aquarium water quality tests and meters .
Some are specific, to measure the alkalinity of the water (pH), the calcareous hardness (KH), its hardness (gH), levels of nitrites (NO2), nitrates (NO3) and ammonia (NH3).
In addition to the tests aimed at measuring each of the parameters, there are another series of Analysis Kits that serve to measure all the parameters.
Its effectiveness varies from one model to another, the strip ones being the simplest, but least reliable.
Hard water and soft water, equivalence of degrees DH to ppm
|Grades DH||Equivalence in ppm (parts per million)|
|0-4 DH||0-70 ppm very soft water|
|4-8 DH||70-140 ppm soft water|
|8-12 DH||140-210 ppm soft water|
|12-18 DH||210-320 ppm fairly hard water|
|18-30 DH||320-530 ppm hard water|
KH and GH
Continuing with the reading of the aquarium tests, we will have to measure the hardness of the water, they offer us two different parameters: KH and GH.
What is the KH?
KH is known as the temporary hardness of water and measures the amount of carbonate ions. When you talk about alkalinity of water, you are referring to KH.
The calcareous, carbonate or KH carbonate hardness is due to the presence of calcium, magnesium, sodium carbonates and other mono or bivalent metals.
Bicarbonates play a very important role as a buffer or buffer for pH regulation.
It can be said that with a high KH level, the aquarium water will be more stable in its PH and will have a greater capacity to neutralize possible imbalances.
A high KH (from 4) helps us so that the PH does not move abruptly and remains stable.
KH and PH usually follow the following relationship:
- KH less than 2 ° reveals little carbonate presence. The PH is unstable, changes from very acidic to very alkaline water can occur quickly.
- KH between 2º and 4º, the presence of carbonate is optimal so that the PH remains slightly acidic, around 6.5.
- KH between 4º and 6º, offers ideal carbonate readings to stabilize the alkaline PH between 7 and 8.
- When the KH is higher than 6, it shows a high presence of carbonates, being able to maintain an alkaline PH higher than 8.
Raise or lower the KH
Sometimes it may be necessary to raise or lower the alkalinity of the water , to in turn modify the PH of the water.
- Raise the KH of the water. Add baking soda or commercial products to the effect.
- Lower the KH of the water. Add reverse osmosis water, mineral water or adding commercial products.
What is GH?
GH measures the total hardness of the water, the amount of calcium and magnesium salts in the water. These salts come in the form of sulfates, chlorides, carbonates, or bicarbonates.
It can be said that GH is the sum of KH (carbonates) and everything that is not carbonates.
When in aquarium hobby reference is made to the hardness of the water, if a certain species prefers soft or hard waters, we are talking about GH and not KH.
It is important to take these parameters into account, because a hard water fish will not be affected by living in soft water, but a soft water fish will have problems living in hard water.
How can I modify the GH of my aquarium?
The usual thing when we are starting to cycle the aquarium , is that we have problems to stabilize the different parameters, including GH.
Also GH can be altered when we introduce new aquarium stones , decoration, aquarium sand or a new substrate.
- If we need to increase the GH, we can add rockery limestone, calcium carbonate (GH and KH will be increased), adding calcium or magnesium sulfate.
We can find commercial salts that will help us raise GH. Another trick is to add calcium for turtles.
- If we need to reduce GH, we can make frequent water changes, add reverse osmosis treated water or mineral water.
Another way to lower GH is to use peat in your aquarium filters and as a last resort, water softeners.