How To Soften Aquarium Water (FAST)

How To Soften Aquarium Water (FAST)

Most fish species live in particular water conditions. They cannot tolerate a wide range of pH, temperature, and, most importantly, water hardness. If you are a beginner in the fish-keeping hobby, you must pay extra care and attention to the water hardness your fish can take. To keep fish healthy, it is crucial to re-create the environment they live in in the wild. This involves fish from various water bodies like fast-flowing rivers, swamps, vast oceans, and stagnant streams. Each of these places has a different water hardness and flow.

If the water is too hard, you will have to soften it to bring it to the appropriate level. 

Most fish that we keep in tanks are bred in captivity, and so they have a higher water hardness tolerance than the ones in the wild. 

Let’s understand what water hardness is, how it occurs, how you can test it, and how to soften the water hardness in your fish tank to make it more comfortable for your fish.

There are also different methods to soften water, based on the tank size. Take a look at this guide to check the types of small tanks and decide which way works best for you.

What Is Water Hardness?

Water hardness is the number of dissolved minerals present in the tank water of your fish. All water has some amount of minerals in it. Water hardness tests focus on calcium, magnesium, and carbonate. 

If these minerals are present in concentrated amounts, it makes water harder. 

To test the water hardness, your testing kit will use two parameters: measuring the General Hardness (GH) and the Carbonate Hardness or the Alkalinity (KH) of the water.

General Hardness (GH) decides how much calcium and magnesium are present in the water. The unit of measurement for GH is dGH (degrees of General Hardness) or ppm (parts per million). 1 dGH is equal to 10 mg (or 17.84 ppm) of calcium oxide per liter of water.

Carbonate Hardness (KH) decides how many carbonates and bicarbonates are present in the water. The unit of measurement for KH is dKH (degrees of Carbonate Hardness) or ppm (parts per million). 1 dKH is equal to 17.86 mg (or 17.86 ppm) of calcium carbonate per liter of water.

The General water hardness usually ranges between 10 to 400 mg per liter of water. As mentioned earlier, different places have different water hardness levels. For instance, African rift lakes have 500 mg of general water hardness! Some areas, such as the Amazon basin, have only 10 mg of general water hardness per liter.

If the fish from both these places are put in the same tank with a middle range of water hardness, they will suffer a lot. This is why it is crucial to have the same water hardness that the fish survive in their natural habitat. 

Most soft water fishes can survive more challenging water, but it will be pretty difficult for you to get any fish to breed in water harder than what they live in.

How Does Water Become Hard?

What could be the reason for the tank water to become problematic? The answer to this is nature. Water hardness is a natural phenomenon that appears as the water passes through rocks such as dolomite or limestone. As a result, the limestone deposited in the soil mixes with the water and increases its hardness. It also causes the number of dissolved minerals already present in the soil to rise.

Water hardness depends on the water’s path until it reaches the tap in your home. On the way, these deposits keep increasing and the water hardness level rises. The water hardness of everyone’s tap water is different. This is why you must dechlorinate and soften the water before introducing it to the aquarium.

If you fail to achieve the desired water hardness, your fish will suffer from diseases.

This chart will help you determine the water hardness level you should achieve, based on the fish needed, in your aquarium water.

Water Hardness General Hardness (GH) Carbonate Hardness (KH)
Very soft 0-4 dGH 0-4 dKH
Soft 4-8 dGH 5-7 dKH
Slightly hard 8-12 dGH 7-8 dKH
Moderately hard 12-18 dGH 9-12 dKH
Hard 18-30 dGH 13-20 dKH
Very hard More than 30 dGH More than 20 dKH

Ways To Soften Aquarium Water

It will prove to be tricky for you to find the correct method to test the water conditions of your tank in the beginning. But one way that you can identify your tank’s needed water hardness is by being through with your testing. Keep a log of daily GH and KH readings from your test kit, which will show you the fluctuations that take place. You can then arrive at the perfect number and soften your tank water.

There are a number of ways to do so, but here are some of the best and most reliable methods:

Using Peat Moss Filters

Peat Moss filters are one of the best solutions to reducing the water hardness. They work in a similar fashion like Driftwood. They bind the calcium and magnesium ions in the water through a method called ‘chelation’. This ultimately softens the water. This process is very similar to demineralization.

Peat Moss Granules

While softening the water, peat moss will also release acids like tannic and gallic acid. This is how the KH and the pH levels decrease. 

You must take some precautions before you use a peat moss filter. Be sure to boil it for two or three minutes so that any parasites or bacteria present there will die.

Peat moss will make your water yellow. To prevent this from happening, you can soak the peat in clean water for some time after it is done boiling.

There are three different ways to use peat moss to lower the water hardness of the tank.

If your tap water is not suitable for the fish, peat moss will help you to soften it. To add peat moss and filter the water, first, boil peat moss so that all the pathogens die on it. After that, drain the remaining brown water, and fill a bucket of tap water. Put peat moss on it and let it sit for a couple of days. Use this water to perform a partial water change in your tank. You will notice a vast difference in the water hardness. 

Another method is to use peat moss in the form of a filter. To do this, wrap it around a mesh bag or a net. The bag needs to be small to fit into your filter. Boil the bag just like the earlier method and allow the peat to cool down. Once it is colder, remove the dirty water and put this bag behind the filtering pad.

The last method is to add peat moss to the tank directly. You will need to boil and let it cool down like it was described earlier. Be sure to place the bag in an area where water circulation happens the most.


Driftwood and peat moss are similar in the sense that they soften water with the use of tannic acids. These tannins are harmless to the fish in the tank. The acid can also boost the health of the fish and protect them from probable infections.


Driftwood is an environmentally viable option because it is made entirely through the fossilization of trees over millions of years. 

But, driftwood also has its side effects. Driftwood can turn your tank water brown. Sometimes, some parasites might also enter the tank through the driftwood. You will have to observe the driftwood to ensure that it does not develop any fungi.


Rainwater is the most effortless method of lowering the water hardness in your tank. Rainwater is free, but before adding it to your tank, make sure to test it once using a testing kit. The container in which you keep the rainwater must also be clean. You can choose a suitable rainwater harvesting method to collect as much clean water as you can.

Remember that even rainwater can have many impurities, especially if you live in a polluted vicinity. It is better to go for other methods like peat moss or water softening pillows in this case.

Water Softening Pillows

These are what they sound like. They are chemical-based media that can help you keep water hardness levels in check. These pillows work through an exchange of materials. They release sodium ions into the water and absorb the minerals from it. The best part about them is that you can reuse them whenever you need them. To clean the pillows before the re-use, just soak them in a salt and water solution for a couple of hours. 

Water Softening Pillows

These pillows are the best for lowering the pH of a smaller tank. But using them in more giant tanks is a hassle because it will take too much time.

Reverse Osmosis Method

Reverse Osmosis is a process that is commonly used in the fishkeeping hobby to keep the tank water pure. The water gets pushed through a membrane (like a filter) through this method, where most of the impurities go away.

Reverse Osmosis

The membrane includes blacking systems for calcium and magnesium, which softens the water to a great extent.

Even though this is a little pricier than the other options, it is a worthwhile investment if you have a large-sized tank. This option is more reliable and thorough than the others.

How To Test Water Hardness In Aquarium Water?

You can test the water hardness of your tank at home by using a good aquarium testing kit. These kits are more reliable and developed specifically to measure water conditions in the fish tank. You will receive readings on the test kit, using which you can change the water hardness.

You can choose from two options if your water hardness reading is high. You can change the fish you have in the tank and replace them with those comfortable with that water temperature. Or, you can use any of the methods mentioned above to soften the water.

To Test General Water Hardness (GH)

To measure the general water hardness, you will need a GH testing kit that explicitly measures calcium and magnesium in the water. Using the table given above, calculate the reading. If you get a lower value than eight dGH, it means your water is softer, whereas a reading of 12 or more will indicate hard water.

To Test Carbonate Water Hardness (KH)

To measure the carbonate water hardness, you will need a KH testing kit that measures explicitly carbonates in the water. If the water is alkaline, it will keep altering its pH from time to time. If you get a high KH reading, it means that your water is resistant to pH fluctuations. This is a good sign as it will prevent unstable water conditions. But, if the KH values are low, your water will keep changing in pH and put your fish at risk.

If your KH levels drop below 4.5 dKH, keep a close eye on the pH and use methods to bring down pH levels, as mentioned in this guide.

Freshwater and Saltwater aquariums should ideally have water hardness: Freshwater aquariums should have a KH between 4 and 8 and a GH between 4 to 8. Saltwater aquariums should have their KH and GH between 8 to 12.

Wrapping Up

Keeping water conditions ideal for your fish is vital to keeping them alive. The water hardness, pH levels, nitrate levels, etc., need to be perfect for captive fish. Water hardness is a much more flexible parameter that your fish will adapt to after a certain period. But even so, you must get their water needs right. 

Getting the water hardness right will allow your fish to thrive and encourage breeding, as fish are more likely to breed in soft water. Not only that, but water hardness accuracy will prevent your tanks from getting water stains or any lime deposits.

In the long run, you will save money if you soften your water. Hard water has a greater chance of ruining your equipment such as filters, pumps, etc. Soft water will go much gentler on your gear and protect it from wear and tear.

As you can see, there are many advantages to softening the hard aquarium water. 

Choose the softening method that works best for you and your fish’s needs!

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