How to Soften Aquarium Water

When it comes to rearing fish in a body of water like aquariums, water quality is vital. The quality of water has a direct impact on the life and survival of the fish. If the water is hard or very hard, the chances of your fish surviving are slim, especially if your fish specie isn't trained to survive in such an environment. If the fish isn't compatible with the type of water, you might have a little problem.

So how do you know if a body of water is compatible with a fish specie? If the water is hard, how do you soften water for an aquarium? If your fish is dying or are having issues about softening your water, you are welcome to read this article on how to soften aquarium water.

Luckily for you, you will learn a lot about water softening techniques.

How Do You Determine Whether Your Aquarium Water Is Hard or Soft?

How Do You Determine Whether Your Aquarium Water Is Hard Or Soft?

If you are unsure about the quality of your aquarium water, there are ways to test for that. This is how to determine whether your aquarium water is hard or soft.

Local water company

Technically, this method is more like an alternative one that will cost you some money.

If you don’t want to go through the stress of figuring out how hard your water is, simply contact any local water company around. Better still, take some samples of your water to them for examination. They should be able to tell you if your water is hard or not.

Soapsuds test

This step is more like for DIY persons. We find this method as the simplest among them all. The reason for saying so is because it won't take you more than ten minutes to figure out whether your water has gone hard or not. You stay in your comfort zone and carry out the testing yourself.

So how do you use this test? Get an empty, transparent bottle. Fill two-thirds of it with your aquarium water. Add some quantities of liquid soap, and shake vigorously for a few seconds.

If you see a lot of bubbles in the water, it's clear that you have an aquarium soft water. However, if there aren’t any bubbles and the water looks milky, it’s definitely hard water.

Test kits

Soapsuds test might be useful to an extent, but using test kits is the most reliable method of determining the general hardness of the water.

You can purchase test kits in liquid form, strips, or in a powdered form.

How do you use these test kits? Insert the test strip in a container filled with aquarium water, and wait for a few minutes. Test strips come with color charts, so observe the color change. The corresponding color change in the water with that of the color chart will determine if you have a soft water aquarium or not.

How to Soften Aquarium Water Naturally and Chemically

To most aquarists, reducing the number of mineral contents in the aquarium is of utmost concern. Once in a while, the water in your aquarium may turn hard, and when it does, you need to find a way to soften it.

How to Soften Aquarium Water Naturally and Chemically

Luckily for you, you don't need to go to a great length or find some sophisticated tools and chemicals to soften aquarium water. At first, it may seem tedious, especially if you don’t know how to go about it.

Below is how to soften aquarium water naturally.

Reverse Osmosis

Also known as R.O, this method is quite simple and inexpensive that will soften your aquarium water. It's a process that involves demineralizing the water to create a purer one. The process uses a semi-permeable membrane that traps minerals and other contaminants in the water.

Reverse osmosis can remove metals from water as well.

This method intercepts about 95% of contaminants that are present in the water, making it one of the most efficient ways of purifying water and economical too.

Water Softening Pillows

A water softening pillow is like a mesh or net that helps to soften the water's hardness in aquarium water. These softening pillows contain sodium ions, which, when used, replaces calcium and magnesium in the water. For best results, place the pillows in the filter of the aquarium.

One great benefit of using this method is the mesh can be reused. All you have to do is dip it into a salt solution and place it back in the filter.

Rain Water

If you want to escape the stress of using various water softening techniques, you can use rainwater. Rainwater has so many benefits that one can't simply imagine.

Rainwater is the purest form of water, making it ecologically sound for use as aquarium water. You can drain some of the existing water in the aquarium and replace it with rainwater. All you have to do is make sure you catch enough in your large containers or clean buckets.

You have to be careful about using rainwater if you live in a pollution-stricken environment. Using polluted water will harm the fish in the aquarium. The rainwater to be used is to be clean, devoid of any chemical or industrial pollutants.


Peat, like softening pillows, is a filter that softens aquarium water. Sera super peat has a working mechanism that’s similar to that of water softening pillows as well. The peat filters hard water and stops the mineral content from being present in the filtered water.

There’s another way to use the peat filter. You can soak the granules in water that you plan to use in your aquarium for one or two weeks. After that, use the water in the aquarium. Always boil the peat before usage to remove any additives inside.


Using fresh, clean driftwood is another alternative method of softening water in your aquarium. It may not be as effective as others that were mentioned earlier, but there's certainly no harm in keeping your options open.

Driftwood will make your aquarium brownish unless you soak it in a container before using it in the aquarium. Boil the driftwood before use to remove any toxin that's present. Remember, you are free to leave the brownish color if you want. It wouldn't harm the fishes inside.

Why Should You Soften Your Aquarium Water?

In essence, the reason for softening water is to lower the amount of calcium and magnesium content inside, thereby promoting osmoregulation. Osmoregulation is the balance of salt and water inside the bodies of fishes with those outside their bodies. Osmoregulation, in a nutshell, is a process fish use to survive in water.  

Why Should You Soften Your Aquarium Water?

If there’s an imbalance, it can lead to the death of the fish. This is why you need an aquarium water softener. Calcium and Magnesium minerals in large quantities make the aquarium unconducive for the fishes. Softening the water will make it more habitable.

However, you should know that water that’s too soft isn’t healthy for the fish either. Water contains minerals or electrolytes, and fish need these minerals for proper growth and development and resistance to certain diseases. If the aquarium water is stripped of these minerals totally, you risk the fishes to malnutrition, which may cause their deaths.

Problems That Come With Softening Aquarium Water

Problems That Come With Softening Aquarium Water

Like we stated earlier, water that’s too soft is as bad as hard water. While it is necessary to soften hard water, doing it regularly has some effects. These effects may be short-term or long-term effects.

So what are the problems that come with softening aquarium water?


Converting hard water to soft water may not be that expensive initially, but what happens in the long run? It becomes somewhat pricey. Some methods of softening water are quite costly. Using the rainwater method is inexpensive but difficult. 

High quantity of sodium

Most, if not all, soft water fishes do well in soft aquarium water, but not all of them thrive so well in water with excessive sodium ions. This might lead to an imbalance in osmoregulation, which might kill the fish.

Softening reduces the efficiency of bacteria

Very soft water is acidic, and most bacteria in water do not work in an acidic environment.


Softening hard water in an aquarium can rapidly change the water's pH, which is bad for the fishes. It may cause the fishes to adapt quickly to the changes, which can stress the fishes to death.

Hardwater Aquarium Fish Species

If you are exhausted about softening the hardness of your aquarium soft water for your fish species, there’s another option available. Why don’t you try replacing the soft water fishes with those that thrive in hard water?

Hardwater Aquarium Fish Species

You may be wondering if there are certain types of fishes that survive in hard water. Well, your guess ends here because some fish species do survive in hard aquarium water. Some fishes can survive in both soft and hard water, though.

So if you rear those kind fishes in your soft water, you have just cut down some costs of getting hard water fishes. That sounds perfect!

Examples of hard water aquarium fishes include;

  • Paradise fish
  • Mollies
  • Swordtails
  • Platies
  • Monos
  • Archers
  • Guppies
  • Scats, etc.

Important Information about softened water in aquaria.

How to Soften Aquarium Water FAQs

Why is My Aquarium Water Cloudy?

If your aquarium is cloudy, it could be a sign that the water is hard. All you need to do is remove the minerals that cause the hardness. We have mentioned the methods you can use to soften your aquarium water.

Aquarium Water Change Frequency?

You should change up to 25% of the aquarium water every two weeks to one month. You shouldn’t change more than 30% of the water in your aquarium because you will remove beneficial bacteria in the tank.

What Are the Aquarium Water Testing Kits?

These are testing kits that you can use to determine the hardness of the water. The testing kits come with color charts and come in different forms. 

Will Hard Water Kill Fish?

No, hard water won’t kill the fish if the fish is compatible with the water environment.

Should Aquarium Water Be Hard or Soft?

That depends on the source of the water. Some fishes survive in hard water, while others survive in soft water. You should know if the water in your aquarium is soft or hard. This will go a long way in determining the type of fish to rear.


Now that you know all that needs to be known about how to soften aquarium water, what’s next?

The next thing is to start to implement the methods that are most convenient for you. Scan through all the information written in this article and make sure that you tend to your fishes the best way you can.

You don’t have to be an aquarist or an aquatic expert to be able to learn and implement all the tips mentioned here. These tips will make sure that the hardness of your aquarium water is minimalized.

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