How To Soften Aquarium Water? 7 Safe Methods


While having an aquarium can be a rewarding experience because of the stunning underwater world it displays and the tranquility it provides, it comes with certain challenges, worth the trouble.

For instance, water hardness is a common issue that many hobbyists encounter. No need to fret, though, as this guide is going to be your rescue!

But what exactly is water hardness? What causes it? How do you soften aquarium water’s hardness, and why is it important? If your noob aquarist mind is storming with all these queries, you’re at the right place. Keep reading!


What Is Water Hardness?

Teleporting water into a solid form of matter? No. Obviously, not. Water hardness results from the minerals in your tank water playing hide-and-seek, creating a fuss in the process.

To explain it in chemistry terms, it refers to the number of dissolved minerals, primarily calcium (Ca) and magnesium (Mg) ions, in the fish tank water. Ultimately adding to the hardness of water, thus compromising its quality.

Now, certain fish species find certain hardness levels favorable, neither less nor more. Because if the fish tank water is too hard or too soft, maintaining optimal pH levels gets difficult. Which in turn can drastically affect the well-being of water creatures, including plants.

Different Scales Used To Measure Hardness

Following are the various scales that are utilized to measure hardness in water:

The degree of general hardness (GH/dgH) is used to measure the calcium and magnesium ions concentration in the fish tank. One degree of general hardness is equal to 10 milligrams per liter (mg/L) of calcium carbonate equivalent.

Part Per Million (PPM) measures the total concentration of minerals dissolved (Mg, Ca, and others). One milligram of the dissolved mineral per liter (mg/L) is proportional to one part per million.

The Milliequivalents per liter (Meq/L) measures the concentration of all the ions in water. Similarly, the French Degree scale determines the calcium oxide concentration in fish tanks. One degree of French hardness is equal to 10 mg/L of Calcium oxide (CaO) equivalent.

According to the U.S Geological Survey, generally, 0 to 60 mg/L (milligram perlite) calcium carbonate is considered soft water, moderately hard if it contains 61 to 120 mg/L, hard if it contains 121 to 180 mg/L, and extremely hard if it contains more than 180 mg/L. These readings elicit the Calcium Carbonate Hardness.

Don’t let all this data overwhelm you, as measuring the hardness isn’t that technical. You can employ a user-friendly digital water hardness tester or go for Calorimetric titration using an EDTA solution. Both are simple.

Factors That Affect Water Hardness

The key elements that can potentially contribute to water hardness are listed below:

The type of fish water substrate/gravel or decorations you use can affect the hardness level. For example, limestone or crushed coal can release minerals into the water that end up increasing the water’s hardness.

Don’t fall victim to superficiality, and think beyond the aquarium’s aesthetics. Choose substrate/ decorations that are best for your aqua friends. Also, use an aquarium filter to keep the mineral content in check and water softness maintained.

Are you using direct tap water to fill the fish tank? We’ve got news for you. Firstly, stop doing that! Secondly, tap water is the enemy of aquariums! It contaminates, disturbs the pH level, increases water hardness (by increasing mineral content), and deteriorates the health of species aboding inside. You don’t want that, do you?

Water hardness also depends on how big of a procrastinator you are when it comes to cleaning your fish’s residence. The more you keep it in shape (changing water levels and siphoning), the cleaner and softer the water stays.

It’s also important to note that some species of tropical fish (and a few others) are hard water fish species. Be careful with that, as keeping fish/plants in the wrong water type can recede growth and lead to health problems.

happy fish

How To Soften Aquarium Water

When it comes to softening aquarium water, there are various options you can go for. Chemical filtration media, mineral reducers, pH buffers, and water softeners are among the common ones.

Let’s discuss a few other ways to soften water in detail:

Peat Moss

Peat moss is a natural and colorful (leaves a yellowish tint) way to reduce the hardness of the water. What peat moss does is exchange humic acid for Ca and Mg ions while also releasing tannic and other acids into the water.

Cheap, easy, and quick!

Water Softener Pillows

Water-softening pillows are another excellent way many aquarium keepers use and recommend. They get rid of magnesium, calcium, and soluble heavy metal ions like iron and copper, resulting in light and soft water.

Water softening pillow not only reduces the hardness but also prevents the flaky, white deposit buildup on the aquarium’s bottom. Thus, doubling the lifespan of your equipment. That’s a plus!


Driftwood is an aesthetically pleasing and vibey solution to combat water hardness. It releases tannins in the water that lowers the pH and softens the water over time. Plus, your fish can reenact Finding Nemo or experience an existential crisis in privacy with driftwood in the tank.

Catappa Leaves

Using Catappa leaves, aka Indian almond leaves, is another preeminent way to naturally soften the fish tank water. Their working principle is also based on discharging tannins. You can add them directly or by crumbling them into small scraps (it’s more therapeutic this way).

Reverse Osmosis Water

Reverse osmosis, or RO, effectively strips the water of its harmful heavy minerals (good minerals as well). You can easily find different types of RO units in varying price ranges.


Rainwater tends to be soft and free of minerals that cause water hardness. Therefore, adding rainwater can help soften aquarium water.

Before you take your bucket and head straight to collecting rainwater, keep in mind you can’t introduce it directly to the aquarium either. It contains contaminants and other microorganisms that can pollute the tank. Process the rainwater first, then add it to the aquarium.

Note for the broke aquarists:

If you don’t want to use tap water and are too broke for bottled water, you can rely on mother nature. Use rainwater to soften the tap water, then filter it, and finally, use it.

Distilled Water and Demineralized Water

Distilled water is a really pure form of water without any impurities and minerals. Therefore, using distilled or demineralized water can soften water by diluting the minerals present in the hard water.

You can get it from any local water company (or sneak it from your chemistry lab; no, don’t actually do that).

Why Would You Need To Soften Aquarium Water?

First off, if you have fish species (plants, too) that come from naturally soft water environments, they’re likely to struggle in hard water. Therefore, adjusting water conditions to suit their aquatic habitat is essential for them to thrive and keep being your pretty besties.

Secondly, the pH level and hardness of water are closely related. Inseparable. Without softening aquarium water, you’re going to have a tough time balancing pH. So, softening water is the way.

Similarly, you don’t want a mineral build-up in your tank’s water. It will disrupt living conditions and mars equipment’s efficiency. Hence, to prevent equipment failure and give your fish a healthy and happy life, softening water is essential.

feeding fish

Final Thoughts

If you have softwater fish species and want to see them this happy (just look at that smile), well, you know now what to do.

Want your fish/other aquatic species and the related equipment to stay longer in your life? Time to test the aquarium’s hardness level, then! And soften water if necessary.

Best of luck with your journey!