How To Soften Aquarium Water

There are many stories to tell as a long-term aquarist. There are many things to deal with in the aquarium concerning the fish, water, food, and equipment. If you’re beginning your aquarium journey, there are some things you need to prepare for, including knowing how to soften aquarium water.

Having hard water in your aquarium isn’t totally nice for your fish, especially if you keep soft water fish. The most important thing as a fish keeper is ensuring your fish is safe, healthy, and happy.

So, how do you take care of water hardness issues, and what things should you know about it? 

Well, find out!

What Makes Water Hard?

How To Soften Aquarium Water

A few factors are the causes of hard water; however, it has to do with the water source in most cases. Water hardness varies from area to area, so the mineral content in your geographical location would differ from others.

That’s the source of the problem! 

After that, the other thing that makes your water hard is the substrate material in your tank, especially if it contains limestones. For example, some people use the oyster shell as a substrate to raise water hardness.

Lastly, you might want to know that your aquarium’s calcium and magnesium levels can as well make water hard.

Ideal Water Hardness For Aquariums

The perfect water hardness for aquariums varies, depending on the kind of fish you keep. Sometimes, water hardness is measured by ppm and as dGH other times. That’s okay because one dGH equals about 17.9 ppm.

The general ideal water hardness for different species aquariums are:

  • 4-12 dGH for tropical fish tank
  • 4-8 dGH for a shrimp tank
  • 12-20 dGH for African Cichlids tank
  • 3-8 dGH for discus tank

How To Determine Water Hardness in An Aquarium

Before knowing how to soften aquarium water, you need to be sure that something’s wrong with your tank. You can check your tank’s water hardness through different means.

Importantly, you should ensure you check GH in the tank at least once monthly. So, what’s the best way to check?

  • You can ask a local water company to come to help you check if you don’t feel up to it. This can sometimes be unnecessary if you can check it by yourself.
  • Try the soapsuds test. Scoop water from your aquarium in a container, fill it with liquid soap and shake. If it has bubbles, then the water is soft. If it doesn’t or looks milky, then it’s hard.
  • Use a test kit that is very accurate to check water hardness.

Why Soften Aquarium Water

Water hardness can be tough on your fish. Some fish can hardly survive harsh water conditions and may struggle and eventually die. In this case, you need to ensure you make the water condition habitable for your fish.

With that said, more reasons you need to soften aquarium water include:

  1. It helps soft water fish thrive rather than merely survive. Fish like angelfish, barbs, and gouramis can stay healthy and maintain colorful bodies.
  2. Prevents hard water stains in your aquarium and limescale build-ups.
  3. Protects your equipment from malfunctioning and helps them last longer.

Does Water Hardness Cause High pH?

Of course, water hardness affects pH in aquariums. When your tank is high in mineral content, it can raise the pH and make the water more alkaline. To lower the pH, you first need to resolve the minerals issues.

But this can be tricky because sometimes, high pH can be okay for some fish species, and lowering the alkalinity can affect them. This is why you should be careful when softening aquarium water, so you don’t lower the pH beyond the normal level.

So, ensure you test the water at intervals to be sure the pH is at its ideal level.

Aquarium Water Softening Methods

You need to gradually soften your aquarium water because a sudden change can impact your fish. Also, you need to use safe methods that won’t harm your fish.

The following are some of the water softening methods that will come in handy as you continue as a fish keeper:

1. Use rainwater

One easy and inexpensive way to gradually soften your aquarium water is by using rainwater. You don’t need to source for it, and it comes to you naturally.

Generally, rainwater is soft, but you would still need to test the water you collect. Sometimes, rainwater can be too soft for your tank’s and fish’s condition. When this happens, you can mix it with tap water which contains a little bit of hardness.

Another thing to consider before collecting rainwater is to check your area’s air quality. If the area’s air is polluted, the chances are that the rainwater will be as well, and it can be bad for your fish.

Follow these safety tips when using rainwater to soften the aquarium:

  • Sterilize the container you’re using to collect the water and ensure it’s very clean.
  • Use containers tagged as “food grade” because they hardly contain chemicals.
  • Choose a safe water collection method that won’t contaminate the water.

2. Water softening pillows

Another way to reduce hardness in water is to use water softening pillows as filtration media. It is a chemical way of softening aquarium water.

These pillows contain ion exchange resins that suck metal ions, magnesium, and calcium and release sodium ions in the process. They are also reusable for a long period.

You need to soak the pillows in a salt and water solution for about 2 to 4 hours to reinforce their water softening abilities after each use. In addition, they are most effective for use in small aquariums.

In larger ones, you would need to recharge them every 48 hours, which is a tedious process. In that case, you would need a less stressful and long-lasting solution. 

Here are some water softening pillows to try in your aquarium:

3. Peat moss filter

3. Peat moss filter

Peat moss can do wonders in your aquarium, like softening the water. It does so by capturing calcium and magnesium ions in your water and, in return, releases tannins and gallic acids in the aquarium.

The acid neutralizes bicarbonate and carbonate ions in the water. When using peat moss as a filter, ensure you boil it for about 2 to 3 minutes to remove parasites and other contaminants and reduce excessive water coloring.

After boiling, you can then soak it in clean cold water to reduce coloring. You can use peat moss in the following ways:

  • Soak it in a clean container

You can try this method if your tap water is too hard.

  • First, you boil the peat moss and throw out the brown water. 
  • Then put the peat moss in a clean container containing clean water. 
  • Leave it there for 2 to 3 days. 
  • Test the aquarium’s water hardness and the peat moss container for water quality.
  • Replace tank water with peat moss water during routine change.
  • Use as filter media

Another way to use peat moss is by placing it in your aquarium’s filter system. The water will flow through the peat moss and soften.


  • Put peat moss in a mesh bag.
  • Boil to remove contaminants.
  • Leave to cool in clean cold water.
  • Then place the peat moss mesh bag in the filter.
  • Use as substrate

You can also use peat moss as a substrate in fish tanks. In this case, ensure it’s completely organic and free from chemicals. Then, you need to put it in a mesh bag and soak it for 3 to 4 days to remove the brown color.

You can also boil it to remove contaminants. Afterward, you can then use it as a substrate.

Good peat moss options for you:

4. Driftwood

4. Driftwood

Driftwood and peat moss work in similar ways. They both release acids that neutralize water hardening carbonate compounds. In addition, the tannins driftwood released in the tank can also help boost your fish’s immune system.

However, it can discolor the water and introduce parasites into the tank. This is why you need to decontaminate and sterilize the driftwood before placing it in your tank. 

You can do that by soaking it in a bleach or soda solution for 3 to 4 days. Then you need to clean, trim, and sandpaper it to remove germs and debris. Finally, you can also boil it if you want.

Here are some driftwood options for you:

5. Reverse osmosis

This demineralization process involves using a semipermeable membrane to capture impurities in water. This will help capture calcium and magnesium, preventing them from entering the aquarium.

This is a very reliable way to soften aquarium water. All you need is to get a RO system like:

6. Catappa leaves

6. Catappa leaves

The Indian almond leaves, also Catappa leaves, can reduce water hardness in aquariums. It also contains tannins that help soften water, lower pH, and make aquariums more habitable to your fish.

However, it discolors fish tank water. Also, you need to be careful when using it, so you don’t end up lowering the aquarium’s pH when there is no need to.

Some Catappa leaves options are:

Risks of Water Softening

While water softening is good for some fish, it requires a gradual process. Sometimes, there are some risks attached to softening water in an aquarium, so you need to be highly skilled in how to soften aquarium water the appropriate way.

The following are some of the risks:

  • It can result in excess sodium ions.
  • Can reduce good bacteria efficiency.
  • This May result in rapid pH change, which can affect your fish.


Knowing how to soften aquarium water is necessary as a fish keeper, especially when you keep fish that can’t deal with it. There are many ways you can soften water, and the easiest way is to use clean rainwater if it’s available.

Otherwise, you can use the other methods you’ve read in this article. Your fish’s health is important, so always watch out for your fish!

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