6 Ways To Soften Aquarium Water

Last Updated on 2023-08-26

Hard aquarium water can be a nuisance in certain cases and may be difficult to deal with, especially for beginners. It can have lasting impacts on the health of fish and aquatic plants and can also prove to be fatal for certain softwater fish breeds. Therefore, it is important to monitor and test the water hardness in your aquarium frequently.

So, how can you soften aquarium water? Softening methods include using rainwater, softening pillows, peat moss filters, driftwood, and performing reverse osmosis (RO).

Read on to find out more about softening the water in your aquarium. Happy reading!

What Is Water Hardness?

Simply put, water hardness is the amount of minerals and metals dissolved in water. These metals mostly include calcium and magnesium. If your hands feel soapy and slippery after washing them, then that probably means that the water is hard. As far as aquariums are concerned, water hardness is a very important parameter, one that should be tested and monitored frequently. It can affect the fish and the aquatic plants in your aquarium. Water hardness can even affect your tank equipment! There are two kinds of water hardness that you can test: general hardness (GH) and carbonate hardness (KH). Find out more about them in later sections of this guide.

How To Test Water Hardness In Aquarium Water

There are many ways you can test the hardness of the water in your aquarium. Read on to find out what they are.

Using Strip Tests

One of the easiest and most accurate ways to test the water’s hardness is to use a strip test kit. The kit consists of a strip that can change color depending on the water’s hardness and a chart that will help you determine the hardness based on the strip’s color. To use a strip test kit, take a small sample of your aquarium’s water in a cup and dip the strip into it. Watch out for any changes in the strip’s color and refer to the chart to find out the results.

Using Reagent Tests

The process of testing the water’s hardness using a reagent test is quite similar to that of a strip test. The reagent test kit usually comes with a test tube, a chemical reagent, and a color chart. You take a small sample of the aquarium water (in a separate container), add the specified number of drops of the reagent to it, and wait for it to change color. Refer to the color chart to find out the corresponding water hardness for the observed color change. Throw away the test tube contents after your test; do not pour them back into the aquarium.

Visiting Your Local Fish Store

If you don’t have strip test kits or reagent kits or can’t get your hands on them, another way you can test the aquarium’s water hardness is to take a small sample of the water to your local pet store. If the pet store sells pet fish and aquariums, they’ll be able to test the water sample for you and tell you the results. Usually, pet stores charge a small fee for this, but some even do it for free!

The Types of Hardness

There are two types of water hardness that you can measure. These are General Hardness (GH) and Carbonate Hardness (KH). GH is the measure of the amount of salts and minerals that are dissolved in the aquarium water, whereas KH is the amount of carbonate ions present in the water. GH is really important since it measures how suitable the water is for your fish. High GH levels can affect fish growth and can also be fatal. KH, on the other hand, is important in ensuring the aquatic plants in the aquarium do not die. Since carbonate ions help maintain the pH level of the water within the acceptable range, KH measurements are important.

How Often Should You Test Water Hardness?

Testing both the GH and the KH of your aquarium water regularly is of paramount importance. It should be done as part of your regular maintenance routine and must not be skipped. If you’ve recently set up your aquarium and don’t have much experience with keeping fish, you should test the water hardness daily to ensure the nutrient balance is established. Once you’ve gained a bit of experience and the water has been replaced many times, you can reduce the testing frequency to once every week or even once every two weeks.

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Why Should You Soften Aquarium Water?

Read on to discover a few reasons why softening your aquarium water is important.

1. Hard Water Can Kill Some Fish

Hard water can be dangerous for many fish and may even kill them. If the water has a large number of minerals dissolved in it, it can affect the internal organs of fish, causing them to malfunction. Since fish are extremely sensitive creatures, many of them can only tolerate a certain range of levels of water hardness, and when the water conditions start falling outside that range, the fish can become sick and die. Though this doesn’t happen a lot, you should still monitor the water conditions regularly and take action whenever the water hardness increases.

2. To Ensure Healthy Growth of Fish and Aquatic Plants

Besides killing fish, hard water can severely impact and stunt the growth of fish and aquatic plants alike. Although this situation isn’t as bad as the former, it’s still one that requires prompt action on your part. A sign that hard water is impacting fish growth can be if your fish are experiencing stunted growth and aren’t growing up to their normal sizes. Similarly, aquatic plants can also experience growth problems if they are in the water with an excess amount of minerals.

3. To Maintain an Optimum PH Level

Maintaining an optimum water pH level is very important for the fish. A too high or too low pH can eventually kill the fish. Hard water normally has a very high pH, which means that the water is alkaline. Softening the water reduces the pH, bringing it back to the optimum level.

4. To Breed Soft Water Fish

There are certain breeds of fish that can only thrive in soft water with low mineral content. If the aquarium water is very hard, you cannot put soft water fish in it since they’ll eventually die. Soft water species include Gouramis, Barbs, and Angelfish. Although they can live in hard water, they’ll exhibit signs of distress and have stunted growth. Simply put, soft water breeds cannot thrive in hard water, and you mustn’t put them in your tank if the water is hard.

5. Prevents Water Stains and Mineral Deposits

Hard water also has the potential to affect the appearance of your tank. It can leave water stains that are difficult to get rid of and can also cause minerals to deposit in different parts of the tank. These mineral deposits can scratch the glass tank walls and need to be removed.

6. Protects the Tank Equipment

Softening water is also essential if you want to protect your aquarium equipment. If the water in your tank is hard, it can cause mineral deposits to build up in your equipment, which can then cause it to malfunction. Air pumps, filters, and powerheads can easily be affected by the build-up of minerals and are prone to frequent malfunctions. Even worse, these deposits can also permanently damage your equipment, in which case you’ll have to immediately replace them.

How To Soften Aquarium Water

Here are a few methods to soften your aquarium water.

1. Use Rainwater

Using rainwater to soften your aquarium’s water is one of the easiest and most inexpensive ways to do the task. Usually, rainwater is soft, but if you want to be sure, you can also test its KH and GH levels. Rainwater only works well as a softener if your area has good air quality and isn’t situated near factories or industrial plants. Here are a few other things to keep in mind.

  • The container used for collecting rainwater should be sterile.
  • Place the container in such a way that the rainwater doesn’t get contaminated.
  • Pick a container that won’t release chemicals into the water.

2. Use Water-Softening Pillows

Another way to soften the aquarium water is to use water softening pillows. These pillows are a kind of filtration media that reduce the water’s hardness. The pillows contain special ions that absorb the minerals present in the water. The minerals that get absorbed include magnesium and calcium. The great thing about water-softening pillows is that they’re reusable. To use them again, place them in a salt and water solution for 3 to 4 hours before putting them in the aquarium. These pillows work perfectly for smaller tanks, but if you intend to put them in a larger tank, you’ll need to recharge them frequently.

3. Use Peat Moss Filters

Yet another way of reducing the hardness of your aquarium’s water is to use peat moss filters. Peat moss can be used as a filter media since it can bind metal ions and lower the water’s hardness. One thing you should keep in mind is that peat moss can lower the KH levels and, subsequently, the pH levels since it produces various acids. Before putting peat moss in your aquarium, you should boil it and soak it to remove any harmful substances and contaminants. First, boil it for a couple of minutes, soak it in water, and then wrap it into a filter bag before putting it in the aquarium.

4. Use Driftwood

Driftwood is another effective method of softening your aquarium water. It works in a similar manner to peat moss; it binds metal ions and releases acids into the water. Driftwood also releases tannins, which are good for fish. However, it can bring in contaminants if it is not cleaned properly before being put into the tank. Driftwood also temporarily changes the color of the water to brown.

5. Perform Reverse Osmosis (RO)

Reverse osmosis (RO) is a technique used for purifying water. It uses a semi-permeable membrane to filter out harmful contaminants and other unwanted substances. When used in an aquarium, the RO process can remove excess metals and minerals and subsequently reduce the hardness of the water. Reverse Osmosis is an excellent option if you have a large aquarium and is a reliable and effective water-softening technique.

Frequently Asked Questions (FAQs)

Can You Use Distilled Water To Soften Aquarium Water?

Distilled water can be good or bad for your fish. It depends on what you’re using it for. If you want to change your aquarium water and are thinking of replacing it with distilled water, then that’s a bad idea. This is because it doesn’t have the beneficial bacteria and the required minerals and can thus kill fish. But if you want to use it to soften your aquarium water, then distilled water is a good option since it doesn’t have any dissolved minerals. Read this guide to find out more.

How Do You Soften Hard Tap Water For Aquarium?

To soften tap water for your aquarium, you can use any of the 5 methods previously mentioned in this guide. You can also use distilled water to do the job since it doesn’t contain any dissolved metals or minerals. Check out this guide for more information!

How Do You Soften Water Naturally?

Using peat moss is one of the best ways to soften water naturally. It binds and removes excess magnesium and calcium ions and also releases tannins. Another way you can soften hard water naturally is to use rainwater. If you collect rainwater properly and ensure it’s not contaminated, you can add it to hard water to soften it.


To sum it up, softening hard aquarium water is not as difficult as you may think since there are numerous ways you can do that. In this guide, we’ve mentioned some of those ways, and we hope you find them useful!

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