22-07-2021, 19:34
16 802


Have you recently measured the hardness of your aquarium water and decided that it is too high? Let's check the different water hardness level intervals in degrees of total hardness (° GH) and in parts per million (PPM):

Water hardness

In general, the acceptable range of water hardness is between 3° and 11° GH (50-200 ppm). This range is acceptable for most fish, however, some species, such as African cichlids, may live with higher water hardness.

Water hardness is a vital parameter that must be considered for the well-being of the fish. It would be good if you keep it within a certain range. If the water hardness is related to the water source, you may have to find an alternative source or treat it to achieve the desired softness.

We will try to explain how to soften aquarium water quickly and effectively.

What is water hardness?

Well, you do not need to be an expert chemist to understand water hardness.

The water hardness is simply a measure of minerals dissolved in the water. The hardness is measured in two ways - general hardness (GH) and carbonate hardness (KH). To be precise, GH measures the concentration of calcium and magnesium ions and KH refers to the amount of free carbonate and bicarbonate ions.

Usually carbonate hardness is also called a measure of alkalinity (hence directly related to pH) and when we say water hardness, it is actually total hardness.

How is water hardness measured?

Fortunately, thanks to advances in technology, you don't need to go to a chemist to check the hardness of your water. Instead, you can check it simply by using an electrical device while sitting at home.

Water hardness is a chemical property that is measured by electronic devices with a probe dipped into the aquarium water. These devices give a direct hardness value in units of degree of hardness (DH) or parts per million (PPM). The degree of total hardness (DGH) is indicated at 10 mg/l CaO, which is equivalent to 17.85 ppm.

What is the best GH (total hardness) for your aquarium?

The GH requirements vary from fish species to fish species. Let's look at the ideal range of total hardness you should maintain in different types of aquariums. This list of estimates is only intended as a rough guide. In some cases, a more precise level may be required.

 What causes a water hardness problem in an aquarium?

Several internal causes cause a water hardness problem, but it is usually determined by the water source. For geographical reasons, the mineral content of natural water sources varies worldwide. As a result, the hardness of tap water varies greatly from town to town.

Most aquarists use tap water in their aquariums. So, if the tap water in your house has a high hardness and you use it in your aquarium, the water source creates this problem in the first place.

Substrate materials could be another possible reason for the increased water hardness. If the stones contain limestone, this makes the water harder. However, some aquarists use crushed coral or oyster shells (as a substrate) to intentionally increase the hardness of the aquarium water.

Hardness and acidity meter.

How can I soften my aquarium water chemically and naturally?

There are some easy ways to soften the aquarium water for your fish. Depending on the condition of the original water, you may need to change the water source.

We recommend starting by changing the water parameters in the easiest way possible. If the first step fails, move on to the next one and so on.

1) Peat moss (Sphagnum)

Peat moss is a decomposed and dried sphagnum moss (sphagnum is a genus of moss with approximately 380 varieties), which has a natural ability to soften water.

Peat mosses are available from pet shops for use in aquariums, but some preparations must be made before using them. Untreated peat mosses, when placed in an aquarium, strongly contaminate the water resulting in a brownish appearance. So boil it for at least an hour until the peat moss stops staining the water brown. Another alternative is to soak the peat moss in a bucket full of water for 3-4 days.

Once the preparation is complete, you can apply three different methods to use the peat moss:

Soften the water in an external tank

The first is the simplest way to use peat moss, in which you soften the tap water before pouring it into the aquarium. By protecting it from contamination by boiling or soaking, you can use peat moss to soften tap water in a large tank.

You will need small mesh bags for this task. Place the peat moss as tightly as possible inside the mesh bags.

Place the peat moss bags in a container filled with water and check the DGH and pH frequently (every 12 hours) until the hardness has reduced to the desired value.

Peat moss inside an aquarium filter

Place peat moss inside the aquarium filter as a filter medium. The process of cleaning and bagging is similar to that described above. You will use peat moss net bags as filter bags. To place them inside the filter, you can additionally use fine granules so that the peat mosses adhere tightly to the mesh bags.

Place the moss bags between the filter media and the charcoal filler for greater efficiency.

Peat moss as substrate layer

Using a peat moss layer as a substrate is not a bad idea. You do not need to fill the peat moss into mesh bags, but spread it across the bottom of the aquarium. You need to add another layer of substrate, preferably gravel, laying it on top of the peat moss layer.


  • Natural water softener
  • Effective and easy to use
  • Relatively inexpensive.


The water can turn brown

2) Water softening sachets

Water softening packets contain ion exchange resins which replace calcium, magnesium and soluble heavy metal ions. Consequently, they reduce calcium and magnesium levels in the water to reduce overall hardness.

The good thing is that these ion exchange resins have no harmful side effects on fish or plants. In addition, the softener pouches can reduce white, hard deposits on the surface of the aquarium. Softening pouches are suitable for softening the water in small aquariums.

They are usually small sachets with resin that can be conveniently placed in the aquarium filter. Softener packs must be changed frequently, however, as they lose their effectiveness.


  • Can be used as filter material
  • Suitable for small aquariums


  • Water softening is not carried out in a natural way

3) Snags

In addition to enhancing aesthetic beauty, driftwood is a natural way to reduce the hardness of aquarium water. Snags release tannins, which are a natural water softener.

At the same time, driftwood lowers the pH value to create a slightly acidic, healthy environment for most fish species. And snags also promote the growth of useful bacteria for aquariums.

In particular, Malaysian driftwood with its high tannin content is best suited for softening water. You can buy ready-made driftwood in the shops or collect it from the wild. However, it is best if you correctly prepare the snags before placing them in the aquarium.

With water changes, the tannins will gradually escape. Some snags release tannins even after six months, some after only 2 to 4 weeks. If you test the water and notice an increase in hardness, even if the snags are saturated with water, you may need to replace them.


  • Great decoration
  • Completely natural way


  • Preparation is a challenge.

4) Using rainwater in the aquarium

Now let's move on to looking at alternative water sources, and rainwater is a super inexpensive option. Rainwater is a gift, but unfortunately not for all regions of the world. If you live in a place that gets enough rain, you can use rainwater in an aquarium.

However, it rains unevenly throughout the year. So it would be helpful if you had a device to collect and store rainwater. This could be a large, clean container with a lid in the open air. When it rains, rainwater will flow into it.

Rainwater collection tanks must be clean, sterile and suitable for foodstuffs in order to avoid any contamination. The storage tank must be large enough to store water during the dry season.
Rainwater is a free source of soft water. You can mix tap water with rainwater in the right proportion in order to achieve the desired pH- and DHG-range.


  • Cheap solution
  • The use of a gift from nature


  • Not applicable everywhere

5) Using distilled water

You can buy distilled water for your aquarium. Distilled water is water purified by distillation. In this process, water is turned into steam by boiling, and then the steam is collected and condensed to produce distilled water.

Distilled water contains no minerals. You must mix tap water with distilled water before pouring it into the aquarium.


  • Zero hardness
  • Can be used when mixed with tap water
  • You can buy it in the shop


  • Relatively expensive solution

6) Reverse osmosis (RO / DI)

If the water hardness problem in your case persists, it is better to have a reverse osmosis / deintegration unit. An RO / DI (deionised reverse osmosis) system puts water through a membrane filter unit to produce 100% pure water.

Like distilled water, reverse osmosis water also has zero hardness, which is not suitable for aquariums. So you can partially mix tap water with it or remineralise the water with reverse osmosis by adding minerals.

Once you have purchased a reverse osmosis system, adjusting the hardness and pH of your aquarium water becomes much easier. However, the device can be cumbersome and the installation cost is quite high. Although initially expensive, it saves you money in the long run.


  • Permanent solution
  • Provides zero stiffness
  • Saves money in the long term.


  • High initial cost

Connection between hardness and pH

Yes, there is a direct correlation between pH and hardness. Water with a higher hardness also tends to have a higher pH value. Everyone knows that pH is the most important parameter of water and its neutral value is 7. Acidic water has a lower value and alkaline water has a higher pH value.

The minerals responsible for increasing hardness also contain alkaline anions, so they tend to increase the pH value. Consequently, pH is a good indicator of the health of water, including its hardness.

But a higher pH value is not a concrete indication of higher water hardness. Water can be alkaline for many reasons without increasing its hardness. So, to get a clear picture of the water hardness in your aquarium, you should measure the DH or DGH value.

Found an error or a dead link?

Select the problematic fragment with your mouse and press CTRL+ENTER.
In the window that appears, describe the problem and send to the Administration of the resource.


Dear visitor
No one has left a comment on this post yet! You can be the first!

Users of Гости are not allowed to comment this publication.