How To Reduce Water Hardness in Aquarium

When you start out owning an aquarium, water hardness is the least of the things that are likely to cross your mind. How can water be hard, you ask? And how can you tell if the water is hard?

No matter the question you have, one thing you should know is that a basic understanding of water hardness would improve the general well-being of your fish and make it easier for you to provide your fish with a safe and healthy environment.

How To Reduce Water Hardness in Aquarium

Getting information about how to reduce water hardness in aquariums might not be challenging. However, getting one that you understand and can implement is entirely different.

In this article, you will learn what water hardness is, how it affects your fish and how you can reduce it in your aquarium. You would also understand why you need to take this aspect of owning an aquarium seriously.

Water Hardness? What does it really mean?

Water hardness simply means a high level of mineral content is present in the water. This mineral content is usually calcium, limestone, or any other material. The higher the mineral level, the harder the water is; on the other hand, the lower the mineral level, the softer the water is.

Water hardness also measures the level of minerals found in the water, and these minerals play a vital role for your fish. They help regulate metabolism, develop exoskeleton, develop bones, and encourage ion exchange. 

Generally, your fish needs to be kept in the correct water hardness level to grow and develop as much as they should. The good news is that hard water can be discovered anywhere, even in our homes. 

For instance, the water that flows from your tap could either be soft or hard, depending on the amount of calcium.

Know that hard water does not mean the water is entirely bad, as some fish can survive well in it while others would require soft water for survival. Understanding the one that works for your fish is what you need to know.

If your fish requires less hard water, what are the things you can do to reduce it, but before we learn that. Do you know the correct water hardness suitable for every aquarium?

Know The Correct Water Hardness for your Aquarium

Getting the ideal range of hard water for your fish wrong might cause many problems. This is why you need to know and understand your fish’s favorable natural conditions.

Knowing this would allow your fish to live a healthy life and grow properly without using a lot of energy. It would also inform you of what fish you should keep at various ranges.

1. Very soft water

Very soft water has a range of 0-3°GH/0-50 ppm. Finding freshwater fish that can thrive in this water is very difficult. Still, the likes of the clown killifish are able to survive in very soft water.

2. Soft water

The soft water has a range of 3-6°GH/50-100 ppm. Minerals found in this water are mainly formed from decayed plants called Tannins. 

Fishes that can survive in waters like this are primarily found in South Africa. Some of them include; South American cichlids, angelfish, tetras, and Corydoras.

3. Moderately hard water

The range would be 6-12°GH/100-200 ppm for moderately hard water. This range of hardness is suitable for tropical fishes like mollies, livebearers, betta fish, and platies.

4. Hard water

The hard water range is usually 12-18°GH/200-300 ppm. Species like mollies and platies are likely to survive under this condition if the water condition is kept stable. Still, hardness lower than this range would be suitable for keeping fishes like African cichlids, flag fish, and Congo tetras.

 5. Very hard water

Very Hard Water has a range of 18+°GH/300+ ppm. This range is also called the liquid rock zone because of the high level of several minerals found in the water.

You have to be careful when choosing fish that can thrive under this condition so you don’t hinder their well-being. However, cichlids from Central America and Africa can survive under this condition.  

Knowing the various ranges would help you understand the environmental needs of your fish, but how would you know how hard your water is?

How To Test Water Hardness in Your Aquarium

How To Test Water Hardness in Your Aquarium

One of the most accurate ways to test the hardness of your water is to make use of a good aquarium test kit. The result would determine your next move. If it would be either to:

  1. Find the species of fish that would live comfortably and survive in the water hardness range the aquarium test kit has shown you.
  1. Perhaps you have a desired fish that you would like to keep if the aquarium test kits show that the water is too hard for your fish; Then, you should use the necessary methods to soften the water and make it suitable for your fish.  

Testing The General Hardness (GH) in your Aquarium

You would need a general water hardness test kit to successfully test the General Hardness (GH) of the water in your aquarium. How these tests work is pretty straightforward. The test measures the amount of dissolved calcium and magnesium present in the water.

It has a guide to show you the answer to your result, which is also very simple. Soft water has a low value of 0-8 dGH, while Hard water has a higher value of 9-12+.

Such a simple way to check the general hardness in your aquarium water.

5 Easy Ways to Reduce Water Hardness in Aquarium  Hurting your Fish

Softening your aquarium water can be a bit of a challenge. Following instructions closely will be a lot of help to see you through this process.

Note that as much as reducing the hardness of your aquarium water to the level that fits your fish is important, it is also crucial that you ensure that the water limits are also stable and are what your fish is used to.

One of the best ways to ensure stability in the water parameters is by taking note of the general hardness (GH) and the Alkalinity hardness (KH) using your testing kit.

Doing this would ensure your fish doesn’t experience any adverse effects due to unstable water.

With that in mind, here is the first way to reduce water hardness in your aquarium.

1. Using RainWater

If you are looking for a good and easy way to reduce water hardness in your aquarium and wouldn’t cost you money while still giving you good results, then use rainwater.

The GH and KH level of the rainwater is not usually high, making rainwater naturally soft. However, that doesn’t mean you shouldn’t test it to be sure.

Here is how to use rainwater to reduce water hardness in your aquarium;

  • Ensure that you are using a clean container to collect the water.
  • Containers used for food are ideal; they do not hold on to harsh chemicals.
  • Collecting rainwater falling on the roof and flowing down isn’t the way to go.
  • Come up with a way to collect rain while preventing contamination. You can place the container above the ground, right in the middle of the rain, where you can safely monitor it.

Using rainwater is favorable for people staying in areas where rain falls regularly and isn’t prone to pollution due to environmental hazards. If this is not the case for you, try the other methods.

2. Using Water Softening Pillows

Water softening pillows is a chemical filtration media used to reduce water hardness in your aquarium. The water softening pillow has ion exchange resins that soak magnesium, calcium, and other heavy minerals.

How it works;

  • Prepare a brine by mixing salt and water together in a bowl.
  • Soak the pillow in salt and water solution for about two to four hours.
  • Place it in the aquarium filter where water flows from into the aquarium
  •  It would walk for 48 hours, after which you must recharge by following the process from the beginning.
  • Keep it away after use. Don’t let the pillow dry out when storing.

Using the water softening pillow is appropriate for using a smaller aquarium. Using this method for a large aquarium can be time-consuming and stressful.

3. Try Reverse Osmosis

Reverse osmosis is another method through which you can reduce the hardness of the water in your aquarium.

This method is the process of removing minerals from the water in order to purify it. Basically, it blocks large minerals like calcium from residing inside the water, making the water soft.

You can get a reverse osmosis system attached to your tap water to make it soft. Since the water no longer contains minerals, pour it into the aquarium to dilute the hard water and make it softer.

4. Using Driftwood

Driftwood releases acid called Tannic into the water that subdues carbonate compounds. However, tannic does not harm the fish in any way, instead, it is beneficial such that it boosts the fish’s immune system and fights against fungal infections.  

The use of driftwood works well for reducing water hardness but produces a brownish-colored tinge in the water, which you might not like. Suppose you don’t decontaminate it by boiling properly, It might be a source of parasites in your aquarium, and it can also breed harmful fungal.

5. Using Peat Moss

Peat moss can also be used to effectively reduce the hardness of your aquarium. What the peat moss does is that it binds and removes minerals as water passes through it. 

Aside from that, peat moss produces gallic acid and tannins, which are suitable for your fish. But there are things you must note before using peat moss:

Before using it, make sure you boil it for two to three minutes so that you can remove parasites and any possible contaminants.

How does this work?

  • Boil it to prevent the possibility of it turning your tank water brown.
  • You can leave the peat moss at the bottom of the container filled with hard water for two to three days to make the water soft.
  • Test the GH and KH to ensure that the quality of the water is stable.
  • Replace the water in the aquarium with it when doing your regular cleaning.

Other ways to use the peat moss to reduce water hardness in your aquarium

  • You can put the peat mass where your aquarium filter is and let the water flow through the peat, softening the water.
  • You can add the moss directly into your tank; just make sure you boil it well and place it on a side where it will get lots of water.


Water hardness is a very sensitive part of owning and taking care of an aquarium. So, you shouldn’t take it lightly, pay attention to the hardness level of your water and take appropriate measures where needed with any of the methods made available to you. Go on and share this article with as many as you feel might need it.

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