Aquarium Care: How to soften water in a home aquarium or fishbowl!

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.

It is widely accepted that over 97% of all living animal species require clean and healthy water to survive. However, the quality of water in aquariums is not always up to par with this standard. Aquaria contain hard water, which can harm fish and other aquatic life by reducing their immune systems.

To reduce these problems, aquarists should learn how to soften the water in their aquariums. Using this article, we will provide tips on softening aquarium water and what methods are most appropriate for various tanks.

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.

How Do You 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.

Measure the PH value of your water

Most people have access to a digital meter that allows them to check the PH of their water. Alternatively, you could also buy a cheap glass bottle with a built-in PH gauge.

Determine the Specific Gravity of your water

Using a refractometer, you can calculate the SG of your water. Refractometers are inexpensive and easy to operate. They work by comparing the index of refraction between two liquids, usually air and water. By calculating the difference in the indices of refraction, you can determine the density of the liquid being measured. 

When you cannot distinguish between the two, it is best to consult a water hardness tester or use a pH test strip.

Test with soap suds

If the soap turns colors in your aquarium, it is hard water. If the soap does not turn colors in your aquarium, it is soft water.

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.

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.

How to Soften Aquarium Water Naturally and Chemically

Below is how to soften aquarium water naturally.

Reverse Osmosis

Reverse osmosis is a method of purifying water by forcing it through a semi-permeable membrane. Pure water passes through the membrane as long as the pressure applied remains constant. Reverse Osmosis units come in both manual and automatic versions. While they are good for treating large volumes of water, they cannot handle small liquids. It would be better to pour boiling water directly onto the tank if you soften only a few gallons of water.

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 is a type of soil composed primarily of partially decomposed plant material. It can be used in aquariums to help soften the water and reduce the number of ammonia and nitrite spikes. However, peat is not recommended for tanks with fish that need more specific and stable water chemistry. Peat tends to break down quickly, releasing nitrogen into the environment. So, it is advisable to avoid using peat unless necessary.


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.

Use baking soda

Baking soda has been used since ancient times to treat many ailments. Baking soda contains sodium bicarbonate, which helps neutralize acidic conditions in the body. Aquarium water allows plants and fish to absorb nutrients by removing excess calcium and magnesium ions. You can dissolve one teaspoon of baking soda in two cups of warm water. Let the solution stand overnight, and then filter out any sediment at the bottom of the container.

Hard water fish to soften water in the aquarium

Aquarium fish need a certain amount of "hardness" in the water to survive. If you have hard water, it's important not to over-filter or use too much salt in the water. If you have soft water, it's important to use caution when introducing fish into your aquarium. pH levels are important to some types of fish, so know what kind you're getting before getting any new ones.

Other ways to soften water in the tank

There are several other options available for softening water in your aquarium. These include:

Using activated charcoal filters

Activated carbon filters are effective at removing harmful chemicals from the water. Although they do not eliminate them, they make sure that there aren't too many left in the water. Added vinegar or lemon juice

Adding either vinegar or lemon juice to the tank will increase the pH levels of the water. A higher pH means less acidity so that the water will become much safer for fish and other marine creatures.

Filtering the water manually.

If you prefer to take matters into your own hands, you can perform a simple filtering process on your own. Pour filtered water back into the tank after each cleaning session.

 Addition of Magnesium Sulfate

Once the water has been softened, it should be tested again to ensure that the correct hardness level was achieved. You may want to try the water every few days while adjusting the dosage of MgSO4 accordingly. As mentioned above, the easiest method to achieve the proper hardness level is to add Epsom salts to the tank.

If you choose to use Epsom salt instead of magnesium sulfate, remember to adjust the amount according to the specific gravity of the water. For example, if the water's specific gravity is 1020, you would need 20 grams per gallon of Epsom salt.

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.  

To keep your fish from dying, you should soften the water in your aquarium. There are a few reasons for this:

Why Should You Soften Your Aquarium Water?

Hardness Levels Affect Fish Health

As discussed earlier, hard water causes several harmful effects on fish. These include decreased immunity, poor digestion, and increased stress. Hard water also increases the risk of disease outbreaks among fish. Because of this, you must regularly monitor the hardness of your water and take action whenever necessary.

Reduce Chlorine Use

To prevent bacteria from growing in pipes, chlorine is often added to municipal drinking water. This is good, but too much chlorine can kill beneficial organisms like nitrifying bacteria. Most municipalities recommend 1 ppm free chlorine when using tap water to prevent microbial growth. The problem is that even though this concentration is safe for humans, it is extremely toxic to fish. To avoid killing off valuable microorganisms, try reducing the amount of chlorine in your tap water.

Increase Plant Growth Rate

Plants need certain minerals to flourish. One mineral that helps plants grow faster is calcium carbonate. Unfortunately, CaCO3 dissolves very slowly in hard water. As a result, plants do not get enough nutrients to develop properly. If you want to speed up plant development, you must add extra calcium carbonates into your tank.

Improve Cleaning Efficiency

If you live in areas where rainfall is heavy, then you know that hard water forms naturally. Even if you don't experience any rainstorms, the hard water still builds up in your home due to evaporation. Hard water contains more salt than regular tap water, so filtration takes longer to remove impurities. By softening your water, you'll be able to improve the efficiency of your filter system.

Prevent Scale Buildup

Calcium ions form insoluble compounds, called calcite or aragonite, when they bind together. Calcium ion accumulation leads to an imbalance between positive and negative charges in the body. A negative charge deposits itself on surfaces like rocks, gravel, and plastic parts of your aquarium. Over time, this buildup can clog your plumbing and damage your equipment.

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.

Problems That Come With Softening Aquarium Water

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?

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.

Hardwater Aquarium Fish Species

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.

Risks and Benefits of soft water in an aquarium

Soft water is more likely to have small amounts of dissolved salts, which can harm your fish's health. However, soft water can also provide many benefits for your aquarium. It may reduce the amount of chlorine needed, increase the rate plants grow, and give a more natural environment for your fish.

Soft water does tend to make cleaning easier, but there are risks associated with its use. Some types of algae thrive on high levels of chlorides, so soft water may encourage the growth of green algae.

Also, when used improperly, soft water can lead to scale buildup inside the filters. Finally, soft water tends to promote bacterial growth, especially during warm weather months. Therefore, only experienced hobbyists should attempt to maintain soft water conditions.

Water Softening Risk

You want the best for your fish, but you might not know that an overly soft aquarium can be bad news! So, let's learn about the risks of water softening and how to keep things safe for your fish.

The factor of pH

When dealing with water chemistry, one factor that should never be overlooked is pH. A high pH value means that the water has more Alkalinity than normal. Alkaline waters have been known to cause stress on fish by causing changes in behavior and physiology. It also causes corrosion in metal objects used in the aquarium. For example, aluminum tanks may become discolored and rust. Corrosion could lead to leaks and cracks in the walls of the tank.

Soft water is full of minerals and metals, which can lead to a rapid change in pH. This means that you will have to test your pH levels more often and use a chemical buffer to counteract the changes. 

Seldom Fish-Friendly

If you don't take care of your fish properly, you'll probably find that they die sooner rather than later. If you do nothing else, try to avoid using tap water if possible. Instead, look into purchasing bottled spring water or reverse osmosis purified water. Both types of water are great choices for keeping fish alive. They both remove impurities from the water without altering its taste.

But wait! It does not need to be this way. There are water softeners that produce soft water that is always fish-friendly. You can now enjoy a happy fish tank and happy family, all thanks to these water softener systems.


One thing that most people forget is that adding chemicals to the water isn't cheap. The chemicals are going to cost you whether you choose natural or synthetic. Hard water is not removed by natural products such as baking soda or vinegar. Synthetic products work better, but they cost much more. The good news is that you only need to buy what you need. Once you've softened the water, you can save the rest for future uses.

Say goodbye to expensive soft water! Save your cash and convert your hard water with some chemicals, or collect rainwater. Now you're ready to save on water softening, and that means a whole lot more money for the fish!

Excess Of Sodium Ions

Sodium ions are very harmful to fish. These ions make the water salty and increase the risk of disease. To prevent sodium ion buildup, add an acidifier to your water. Acidifiers neutralize excess sodium ions so that they cannot build up in the water.

Wow! It looks like there are some excess sodium ions in the water around here. So, not all fish will do well in soft water conditions. If you have a water softener, it will probably work by adding sodium to the water. That way, the sodium ions will be at a normal level.

Efficiency Of Bacteria

Bacterial filtration works well when combined with mechanical filtration. Mechanical filtration removes large particles from water, whereas bacteria filter smaller particles. When combining the two, you get a system that produces cleaner water faster. But remember: too much bacterial activity can harm the health of your fish. Make sure that you monitor the amount of bacteria present in your water.

When you have hard or alkaline water, filter bacteria are at their peak. But in soft water that is acidic, they may not work at all! Therefore, you should consider having many filters installed in your aquarium. One filter would handle the larger particles, while another one handles the small ones.

Fish Tank Water Hardness Fully Explained: Don't Kill Your Fish!

How to Soften Aquarium Water FAQs

1. 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.

2. 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.

3. 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. 

4. Will Hard Water Kill Fish?

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

5. 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.

6. Does Driftwood Soften Aquarium Water?

Aquariums are typically filled with water as soft as a pond or as hard as a rock. In some cases, aquarium owners may use driftwood to create the ideal softening effect needed for the aquarium's ecosystem.

7. Will softening the aquarium water harm my fish?

The aquarium water will probably not harm the fish but softened, or hot tap water could do some damage.

8. Is soft water safe for freshwater aquariums?

Soft water is not safe for freshwater aquariums. Soft water contains dissolved minerals, such as calcium and magnesium. These minerals can create toxic levels of these substances in soft water, causing harm to fish and other aquarium animals.


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.

In conclusion, there are many ways to soften water in aquariums. Some of them involve changing out filters, while others involve adjusting the pH level of the water. Regardless of which method you choose, make sure that you follow proper procedures to avoid harming yourself or your fish.

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