How To Soften Aquarium Water In 6 Steps (Pretty Effective)

Have you measured the hardness of aquarium water recently and thought it’s too high? Let’s check different spans of water hardness level in degrees of general hardness (°GH) and parts per million (PPM):

soften hardwater for aqiarium

As a devoted and passionate aquarist, you would love to provide the best possible home for your fish. But the reality is that water hardness concerns you, so you are searching for a suitable solution. The hardness of the tap water you use in the aquarium can vary from source to source, beyond your control.

Water hardness is a vital parameter you should consider for fish’s wellbeings. It would help if you kept it within a specific range for particular species. If water hardness is because of the water source, you might need to find an alternative source or treat it to achieve the desired softness.

In this article, I will try to explain how to soften aquarium water quickly and effectively. Keep reading.

What Is Water Hardness?

Well, it is not necessary to be a master in chemistry to understand water hardness. 

Water hardness is simply the measure of dissolved minerals in the water. The hardness is measured in two ways: General Hardness (GH) and Carbonate Hardness (KH). To be specific, the GH measures Calcium and Magnesium ions’ concentration, while the KH refers to free Carbonates and Bicarbonates ions quantity.

Typically the Carbonate hardness is also referred to as a measure of alkalinity (hence directly related to pH), and when we say ‘water hardness,’ it refers actually general hardness.

How Is Water Hardness Measured?

Luckily, because of technological advancement, you don’t need to go to chemists to test the water hardness. Instead, you can test by yourself simply using an electric device sitting at home.

Water hardness is a chemical property and measured by electronic devices immersing the probe in the aquarium water. These devices will give a direct value of hardness by the unit of either Degree of Hardness (DH) or Parts Per Million (PPM). A degree of General Hardness (DGH) indicates 10 mg/L CaO, equivalent to 17.85 ppm.

What Is The Best GH (General Hardness) For Your Aquarium?

Best Hardness For your aquarium type

The GH requirement differs for various kinds of species. Let’s look at the ideal range of general hardness you should maintain in different types of tanks. This list of estimations is for a rough guideline only. In some cases, a more precise GH level would require.

What Causes The Aquarium Water Hardness Problem?

A few internal reasons cause the water hardness problem, but commonly, it is determined by the water source. Due to geographical reasons, the mineral contents in natural water sources are not uniform throughout the world. As a result, tap water hardness varies heavily from town to town.

Most aquarists use tap water in their aquariums. So, if your local water supply is providing hard water and you are using it in the aquarium, the water source creates such a problem in the first place.

Another possible reason for water hardness escalation could be the substrate materials. If the substrate rocks contain limestones, it contributes to making the water harder. However, people use crushed coral or oyster shells (as the substrate) to intentionally raise the aquarium water hardness.

How To Soften Aquarium Water Naturally And Chemically?

If you feel the necessity to soften the aquarium water for your fish, I can propose a few simplest ways to do it. Depending on the source water condition, you might need to change your water source.

But it is better to think step by step and not replace the source at first. My recommendation is to start treating your water with the easiest method. If the first step fails, go to the next, and so on.

1) Peat Moss (Sphagnum)

Peat Moss is decayed and dried sphagnum moss (sphagnum is a genus of approximately 380 accepted species of mosses) having a natural ability to soften water. 

Peat mosses are available in pet stores for aquarium uses, but some preparation works are necessary before using them. Peat mosses come with contaminations and lead the water to turn brown. So boil it for an hour, at least, as long as peat moss leaches brown color. Another alternative is, soaking peat mosses in a water-full bucket for 3 – 4 days, and they will be de-contaminated.  

Peat moss As aquarium water softener

However, once the preparation is done, you can implement three different techniques for using peat moss: 

Soften Water In An Outside Container

The first one is the most straightforward technique of using peat moss, in which you will soften your tap water before pouring it into the aquarium. After warding it off from contaminates by boiling or soaking, you can use peat moss for softening the tap water in a large container.

You will need small-sized mesh bags for the task & nylon sacks nicely meet the purpose. Place peat moss tightly as much as possible inside the mesh bags.

Place peat moss bags in the water-full container and test DGH and pH frequently (every 12 hours) until the hardness downs to the desired value. In established aquariums, add softened water with weekly partial water changes instead of replacing it all at once.

Peat Moss Inside Aquarium Filter

Insert peat mosses inside the aquarium filter as filter media. The cleaning & bagging process is similar as stated above. You will use mesh bags of peat mosses as filter bags. To put them inside the filter, additionally, you can use small fine granules so that peat mosses fit snugly inside the mesh bags.

Before putting peat mosses in the filter, let them cool down completely. Place the moss bags between the filter pad and charcoal media to ensure more effectiveness.

Peat Moss As A Substrate Layer

Using a layer of peat mosses as the substrate is not a bad idea at all. For this technique, no need to fill peat mosses in mesh bags but spread them across the aquarium’s bottom. You need to add another layer of substrate, preferably gravel, on the peat moss bed.

Peat moss materials are fluffy and light so that they will be relocated by water movement without a heavier top layer. The additional gravel/soil layer also helps prevent anaerobic pockets that promote harmful bacteria growth.

Peat moss as the substrate materials absorb minerals to soften water, but the aquarium water might turn brown even though you boiled & clean them well beforehand. I prefer the substrate technique less than the first two.

  • Natural water sofetener
  • Effective and easy-to-use
  • Relatively inexpensive
  • Water may turn brown

2) Water Softener Pillow

Softener pillow As aquarium water softener

Water softener pillows contain ion exchange resins to replace Calcium & Magnesium and soluble heavy metal ions. Hence it reduces calcium & magnesium levels of the water to lower the general hardness.

The good thing is that these ion exchange resins have no harmful side effects on your fish or plants. Additionally, softener pillows are capable of reducing white, crusty deposits on aquarium surfaces. Water softener pillows are suitable water softeners for small tanks.

Usually, these products are small pouches full of resins, and you can place them conveniently in the aquarium filter. But softener pillows need frequent recharging as they lose their effectiveness.

By soaking the softener pillows in aquarium salt solutions for a few hours, you can recharge and reuse them. Follow manufacturer’s instructions to recycle as there might have dissimilarity in methods for individual products.

  • Usable as filter media
  • Suitable for small tank
  • Can be recharged & reuse
  • Not a natural way

3) Driftwood

Besides enhancing aesthetic beauty, driftwood is a natural method to reduce the hardness of aquarium water. Driftwoods release tannins which is a natural water softener.

Simultaneously, driftwoods lower the pH to create a slightly acidic healthy environment for most fish species. And also, driftwood promotes the growth of beneficial bacteria for aquariums.

Specifically, Malaysian driftwood, which is high in tannins, works best to soften the water. You can buy readymade driftwood from stores or can collect it from the wild. But it would be best if you prepared driftwood properly before adding it to the aquarium.

Preparing driftwoods is not a challenging task if you do it systematically. For more help, please read my article on how to prepare driftwood for aquariums.

Tannins will gradually go away during water changes. Some driftwood releases tannins even after six months, some only for 2-4 weeks. If you test the water and see hardness increasing, even driftwoods soaked in the water, you may have to replace driftwood. 

Another common alternative is tannins producing leaves (Indian Almond Leaves) – using these leaves, replenishing will be easy for you. 

  • Excellent decoration plus softener
  • Fully natural way
  • Encourage healthy aquarium
  • Preparation job is tricky 

4) Using Rainwater In The Aquarium

Rainwater As aquarium water softener

Now come to the point considering alternative water sources, and rainwater is the super inexpensive option. Rainwater is a gift, but unluckily not for all areas of the world. If you live in a place where it rains sufficiently, you can utilize rainwater in the aquarium.

However, it does not rain equally throughout the entire year. So it would help if you had the arrangement to collect and store the rainwater. It can be a large and clean container with a lid under the open sky. Whenever it starts raining, you open the lid and let rainwater in.

The rainwater collecting containers should be clean, sterile, and food-grade materials to eliminate any contamination. The storage tank should be large enough to store water for the dry season.

Rainwater is the free source of soft water. You can mix tap water with rainwater in the right proportion to achieve the desired range of pH and DHG values.

  • Very inexpensive solution
  • Utilizing the gift of nature
  • Comes with healthy parameters
  • Not practical for all areas

5) Using Distilled Water

Distilled water As aquarium water softener

You can buy distilled water for your aquarium. Distilled water is purified water through a distillation process. In this process, water is turned to vapor by boiling, and then steam is collected and condensed to get distilled water.

Distilled water is entirely mineral-free as vapor leaves everything behind during evaporation, resulting in pure water. You must mix tap water with distilled water before pouring it into the aquarium.

  • Zero hardness
  • Useable by mixing with tap water
  • You can buy as per demand
  • A bit expensive solution

6) Reverse Osmosis (RO/DI)

RO water As aquarium water softener

If the water hardness problem is persistent in your case, better to have a RO/DI unit. A RO/DI (Reverse Osmosis De-Ionized) system passes water through a membrane filtration unit to deliver 100% pure water.

Like distilled water, RO water also contains zero hardness, which is not suitable for aquariums. So, you can partially mix tap water with it or remineralize RO water by adding minerals.

Once you get a RO system, managing hardness and pH for your aquarium water will be pretty more manageable. However, the unit might be bulky, and the installation cost is a bit high. Though initially expensive, it saves your money in the long run.

  • A permanent solution
  • Provides zero hardness
  • Saves money in the long run
  • High initial cost

Hard Water Fish Species

If none of the above-described methods work, I got a solution for you; get fish species that do well in water hardness. This is the final solution upon the failure of suggested techniques. Still, I think it is good to know about the fish you can keep in a high DGH value.

Moderately Hard Water (6° – 11°) Fish Species


Swordtails are peaceful community fish popular among new aquarists. Most importantly, they don’t have a strong urge for water softness. Swordtails are nice colorful fish. They are omnivorous and grow up to 6.5 inches.


Mollies Hard water fish

Mollies are hardy fish and tolerate a wide range of water hardness. Several species of Molly are popular in the aquarium trade. They are small peaceful community fish and very suitable for beginners also. Mollies are omnivorous fish and grow up to 4.5 inches in length.


Platy fish can live happily with moderately high water hardness. They are small, peaceful, and popular aquarium fish of exotic colors. Platies feel very comfortable in large groups of their same species. They are omnivorous and grow up to 2.5 inches in size. Platies are one of the best fish species to keep in a small aquarium.

Paradise Fish

paradise fish Hard water fish

Paradise fish are small species but aggressive in their behavior. They are not the perfect picks for new hobbyists. However, Paradise fish are attractive for their red and blue stripes and quite okay in high water hardness. They are omnivorous and grow up to 3 inches in size.


Archerfish are amusing characters. They are famous for their ability to shoot down resting insects above the water surface. Archerfish are hardy and sustain water hardness comfortably. Archerfish can grow pretty big in size, up to 12 inches. However, they are peaceful species but tend to eat tiny tankmates.

Hard Water (11° – 22°) Fish Species

African Cichlid

African Cichlid Hard water fish

African Cichlids are colorful, charming, and aggressive like all other members of the Cichlid family. Depending on the species, African Cichlids grow from 3 to 8 inches in size. They nicely cope up with the higher hardness of the water. Cichlids are usually long-living fish and survive up to 15 years.

Why Do You Soften Your Aquarium Water?

You want to soften the aquarium water simply because your water hardness does not meet the ideal condition suggested for your fish species. Some fish species are so delicate that they cannot survive in high DGH, especially, If you have tiny fish or small fry.

Water hardness is associated with alkaline water, and the aquarium water should neither be too acidic nor alkaline. Fishkeepers should keep water parameters in the ideal range to provide a healthy home for fish.

Dissolved minerals (that cause high water hardness) undergoing several chemical processes can cause white, crusty deposits on aquarium surfaces and white film on top of the aquarium water.

Relation Between Hardness And pH

Yes, there is a direct relationship between pH and hardness. Water with higher hardness also shows the tendency to have higher pH. Everyone knows pH is a crucial water parameter, and its neutral value is 7. Acidic water has lower & alkaline water has a higher pH value.

Minerals that are responsible for increasing hardness also carry alkaline anions, and so they have the tendency to increase ph. Hence, pH is a good indicator of the healthiness of water, including hardness.

But a higher pH value is not concrete evidence of higher hardness of the water. The water can be alkaline for many reasons without increasing the hardness. So, to get a clear picture of your aquarium water hardness, you should measure the DH or DGH value.


I know you are very keen to clinch a cozy home for your fish, and the water hardness bothers you. Maintaining good water quality is the utmost priority in fishkeeping. So, you are doing the right thing to explore information on how to soften aquarium water.

Though water hardness is not supposed to be a significant problem causing reason, your effort to provide the best is appreciable. The above tips should be adequate to meet your purpose and make your aquarium journey hassle-free.

Most of my suggested techniques are relatively inexpensive but effective. In my opinion, using peat moss as a softener is the best method to soften aquarium water. But you can pick any of those as per your judgment.

Finally, I would love to hear your opinion on this topic. Please share your thoughts or comments in the below comment box.

Sujit Modak

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