How To Soften Aquarium Water – 5 Easy Ways

Water is an important aspect of fishkeeping. It could be the difference between life and death for the fish species in your fish tank.

But many fish species aren’t hardy enough to survive in an aquarium with hard water. That’s why you should ensure the water is soft because even a day in this type of water can be too much for some fish to bear.

But before you start working on softening your aquarium water, you need to understand why aquarium water’s hardness can be bad for fish.

What’s So Different About Aquarium Water?

While many people discuss water hardness, they barely get into the details of why. But don’t worry; we got you covered. Water hardness refers to the number of minerals found in the water.

If the water is soft, it has a low concentration of minerals. Hard water usually has a higher level of minerals. The dissolved minerals in water can quickly affect your home aquarium’s living and non-living matter. 

Hard water could affect your fish and tamper with their growth. For example, some fish species experience stunted growth and have difficulty adapting to their new environment with hard water conditions. Some tropical fish won’t live longer depending on the water hardness in the fish tank. 

Soft water fish include: 

  • Tetras
  • Barbs
  • Cory Catfish
  • Ram Cichlids
  • Some Rasboras
  • Dwarf Cichlids,

But not all species are bothered by water hardness. Hard water fish species like guppies, mollies, and swordtails prefer harder water in their aquarium.

So if you don’t want to worry about softening aquarium water (too much), choose fish species that are comfortable with hard water for your aquarium.

If you already have fish in your tank that need soft water to survive and you’re wondering why hard water isn’t good for them, here are a few reasons:

  • Water hardness affects the pH levels in the tank. This could make the water more acidic or alkaline than necessary for your fish. 
  • Hard water also affects plants in the fish tank. It could tamper with their growth due to the excess minerals in the water. 
  • As mentioned above, hard water can stunt your fish’s growth, but it could cause serious illnesses too. While the diseases might not be fatal, your fish could become sick and stressed, altering their behavior and reducing their activity in the fish tank. 

How To Test The Water Hardness in Your Fish Tank

While you can take a bottle or a cup of your aquarium water to get tested at your local fish store, you might have to make numerous trips every time you suspect something is wrong.

The best way to test the water hardness in your aquarium is by using a quality water test kit. Some of the best water test kits measure water quality and hardness. This way, you can instantly tell if you have soft or hard water in your fish tank. 

Types of Water Hardness 

Carbonate hardness (KH) refers to the level of carbonate and bicarbonate dissolved in the water. Unlike General Hardness (GH), Carbonate hardness affects the pH levels of the aquarium water. Higher KH levels mean the pH levels are high, and vice versa. This is dangerous to the fish species in your home aquarium. 

General Hardness (GH): This refers to the amount of magnesium and calcium dissolved in the water. High general hardness causes white flaky buildup (limescale) on the tank lid and glass. Although general hardness does not affect the pH level, it could harm fish. 

How To Tell If Your Aquarium Has Hard or Soft Water

  • Very soft: 0-3 GH
  • Soft: 3-6 GH
  • Moderately Hard: 6-11 GH
  • Hard: 11-22 GH
  • Very Hard: 22+ GH

Reasons To Soften Aquarium Water

Most aquarists want to soften their aquarium water so their fish will be comfortable and healthy. Fish need certain water parameters to be met to grow and thrive in their new environment. While most fish species can survive with some hardness in their water, it can be hazardous to others.

So here are some reasons why you should soften aquarium water: 

  • If you have soft water fish, softening the water will be ideal for them to thrive. Although some fish species, like angelfish, can do just fine in hard water, they will not thrive and be at their optimum health version. Softening the water can reduce their stress levels so they can be at their best. 
  • Soft water is good for the fish’s immune system, especially soft water fish. 
  • If you want to breed soft water fish, it’s best to soften the water before embarking on this journey. You want to promote breeding in these fish, so you should ensure they are eating well and relaxed enough to mate in the breeding tank. Slightly acidic soft water will encourage breeding for these fish. 
  • To prevent hard water stains in the fish tank. It can be tasked to clean the limescale build-up from the tank glass. You could end up damaging the aquarium and your view in the process. 

How To Soften Aquarium Water – The 5 Ways

If you used the method above to check and find that the water in your home aquarium is hard, then there are several ways you can soften your aquarium water. Here are five:

1. Water Softening Pillows

The benefit of water-softening pillows is they can quickly remove the extra minerals from your home aquarium. These softening pillows work by attracting and absorbing the minerals from the water. They are filtration media that reduce the general hardness of aquarium water.

water softening pillows

You have to drop them in the water for some time. Some can even remove heavy metals from the water. You can reuse the softening pillows if you soak them in a salt and water solution for about 4 hours. Recharging for larger tanks can take more than 2 days.  


  • Water-softening pillows work quickly to remove minerals from the water. 
  • Some water-softening pillows are reusable. 
  • This method is effective for small fish tanks. 


  • Softening pillows can be expensive
  • You may require many softening pillows depending on how many water changes you do per year. 
  • Using water-softening pillows in larger fish tanks of more than 30 gallons is time-consuming.

2. Rainwater Harvesting

If you don’t always want to have to soften your aquarium water, the best thing to do is harvest rainwater. Rainwater is softer than tap water because it does not contain as many minerals as hard water.

Rainwater Harvesting

If the water is too soft for your fish, you can mix it with tap water. But with rain water, you must ensure your container is as clean as possible. You should also collect the rainwater carefully to prevent any contamination from the surroundings.

The best way to add rainwater to your tank’s aquarium is during the water change. You can swap 25% of the water in their aquarium with rainwater.


  • Rainwater is easily available depending on the season.
  • It’s an eco-friendly way of softening hard water.


  • Heavy industrial areas with poor air quality aren’t the best for collecting rainwater. 
  • Can be difficult to store rainwater due to the risk of contamination.
  • Dependent on weather conditions. You can’t harvest rainwater if it’s not raining enough to get large quantities.

3. Reverse Osmosis

This is one of the best ways to soften water without affecting the health of your fish and plants. An RO system filters out the unwanted particles going through it.

Reverse Osmosis

The water you get is pure and soft for your fish, but can potentially be too soft. Fish still need some minerals in their water to be healthy.

So you need to remineralize the RO water and add it to the aquarium. Some aquarists prefer to mix it with tap water to attain the best water chemistry for their fish.


  • It is a good investment if you have soft water fish.
  • Reverse Osmosis provides pure water for softening water.
  • This method is good for the environment.


  • Reverse osmosis uses a lot of water.
  • It removes healthy water minerals from the water and decreases the pH levels.
  • It is costly to install and maintain RO machines.

4. Using Peat Moss Filters

Peat moss is another good way of softening your aquarium water without affecting your fish’s routine and health.

Peat Moss Filters

This filter media binds calcium and magnesium ions to reduce the water’s hardness through chelation. Although it doesn’t work as fast as the other methods on this list, it is one of the easiest ways to soften hard water. The best way to use peat moss is by adding it to the tank’s filter to increase its effectiveness.

Before using this filter media, you need to boil it for 2-3 minutes to eliminate potential parasites or other contaminants getting into the aquarium water.

Soaking it in clean water can also prevent the aquarium water from turning yellow because it lessens the effect of the tannic acids in the water, but slows down the softening process.

You can find several effective peat mosses online. Using peat moss during every water change will ensure the best water quality for your fish species.


  • It’s a natural product.
  • The peat moss takes 2-3 days to soften the water
  • Peat moss keeps ammonia away from your fish tank. Ammonia is very harmful to fish creatures.
  • Peat moss also helps control the water flow rate in your aquarium.


  • It can cause excessive yellowing of the fish tank
  • If you don’t boil the peat moss, you might get parasites in your fish tank.

5. Use Driftwood

Driftwood works similarly with peat moss by producing acids in the water. Another simple way to soften the aquarium water is to add driftwood to the tank.

Driftwood for softening aquarium water

While most people think that driftwood only acts as decoration, they are also good at softening the water.

Driftwood is a practical and good choice because it releases tannins (tannic acid). While the water could turn brown, it causes no harm to your fish in the tank.  But the tannic acids are responsible for staining the tank’s glass.


  • Tannic acid is harmless to fish. 
  • Tannins are good for the health of the fish. 


  • If you don’t decontaminate the driftwood, it can introduce parasites into the tank. 
  • It could discolor the water for a short period. 
  • If there is no aeration, the tank could easily be fungal-infected. 

Softening Aquarium Water

While checking the water parameters is important for your fish species, what’s important is that the water is stable. And all fish species need certain minerals in their water to be healthy and happy.

If you plan to put invertebrates like shrimp and snails in the same aquarium, they need minerals like calcium to help their shells grow stronger.

So if you have soft water fish, try out the methods above to soften aquarium water.

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