How to Increase Water Hardness in Aquarium

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by Jason Matthews



To keep your fish happy and healthy, it is essential to provide them with the proper water conditions. In some cases, this may mean increasing the hardness of your aquarium’s water. So, how can you increase water hardness in aquariums?

There are many ways to increase water hardness in your aquarium. One way is through the use of tap, crushed coral, and aragonite, for example- these all harm pH levels, so it’s best if you keep them away from anything that needs an even amount like plants or livestock. Another option would be limestone which will provide calcium carbonate deposits inside their bodies and provide nutrients vital enough to support healthy blooded life forms that grow stronger and faster than they usually would without these extra ingredients present.

Luckily, this is a relatively straightforward process accomplished in simple steps. Keep reading for instructions on how to increase water hardness in your aquarium.

Top Ways of Increasing Water Hardness in Your Aquarium

Water Hardness

1.   Using tap water

When it comes to water quality in your aquarium, you should always look for signs of hard or extreme amounts. If your tap has turned out more than just “moderately” complex, then there’s no need to go any further because this could make fish lose their appetite and plants begin dying off quickly- which would leave both parties with less than ideal living conditions.

This explains why it is important to constantly change your tap water frequently. This will better the conditions of your aquarium, making your aquarium fish and plants survive sustainably.

You might be surprised to learn that there are many benefits of using tap water in your aquarium. One significant advantage is that it’s simple and doesn’t need special chemicals or methods. Though this is a modern method, it’s not always the best. Try other ways if you have soft or hard water compared to what comes out of your tap.

2.   Crushed coral

Maybe you’ve never heard of it, but crushed coral can be used to make your water harder. It has a high concentration of calcium carbonate and will raise the pH level in whatever aquarium is hosting it.

You can either position your crushed coral in a media bag or mix it with gravel. When you add crushed coral to your water, both the general and carbonate hardness will increase. The fact that crushed coral contains both GH and KH means it has a very high pH which can be uncomfortable for fish who prefer soft waters with low acidity levels.

Related: See which fish prefers low pH here

3.   Aragonite

Like the most soluble form of calcium carbonate, aragonite contains a lot that aquarium enthusiasts can use. It comes in both rock and sand shapes, affecting your aquarium once added to it.

The ideal type of aragonite you can use to increase your aquarium’s water hardness is oolitic, which comes from the ocean and has been carved into spheres. It liquidizes with just a little bit of flow, so it will be perfect for any type or size of fish in your aquarium that needs more strenuous activity levels.

With its beautiful, crystal clear color and high luster to maintain the pH balance of your aquarium water, it’s no wonder that aragonite is so popular. However, it also has its disadvantages as it only dissolves in freshwater and only works best with a solution that is warm.

4.   Remineralized Water

When water is deprived of its beneficial minerals, it becomes demineralized water. Water that has been remineralized can regain as much of its original hardness. The water will now contain magnesium and calcium, two minerals typically missing from soft water.

The process of adding water remineralizers to your aquarium is simple. All you need are post-filter staples containing either calcium or magnesium, with the most common being calcite that has calcium carbonate, and corosex that has magnesium.

You can always add a water remineralizer after changing the water in your aquarium. By following these tips on softening it with remineralized water,  it’ll be no problem.

5.   Limestone

Hardness is an essential factor in maintaining healthy aquariums. Calcium and other beneficial minerals are released when limestone enters the water in an aquarium, making it perfect for adding balance to your home’s aquarium. Texas Holey Rock is one of the most common types used by cichlid aquarium enthusiasts everywhere.

When adding limestone to an aquarium, you must test the water first. You can do this by taking a sample and seeing what kind of result you get to determine if your aquarium needs some limestone.

Sometimes all you need to do is apply this solution directly below your aquarium before filling it with water or dissolve the powder in a bowl of cool fresh water and add it that way.

Related article: How to reduce water hardness

Frequently Asked Questions

How Do I Adjust the Hardness in My Aquarium?

One of the easiest ways to soften hard water is using a natural “water softener.” You can also take out any minerals in your fish tank with Sera Super Peat or demineralized tap water for this purpose. Lastly, if you’re looking into raising pH levels on acidic water that doesn’t have much mineral content – try adding some pebbles from an alkaline bog.

Does Aquarium Salt Increase Hardness?

We have several different salt grades, but plain aquarium/tonic is rarely suggested. Marine mix will provide much more than this basic solution as it raises pH levels significantly along with increasing carbonate hardness in your aquarium.

What Does Baking Soda Do to Aquarium Water?

pH is an essential factor in aquariums; too low, and the water will be acidic, killing fish. To fix this problem, baking soda has been used as a natural remedy to raise pH levels safely, so they’re suitable for aquatic life.


Aquariums are a great way to bring nature into your home, but they can also be hard to maintain. You have to keep up on the maintenance and ensure that everything runs smoothly, not to kill any of your fish or plants.

To increase hardness in an aquarium, use a water filter that includes a media bed of either crushed coral or aragonite. These minerals will help raise the pH and carbonate levels in your tank.

We hope this post has given you a glimpse of how you can increase water hardness in your aquarium without too much hassle.


Jason Matthews

My name is Jason Matthews, and welcome to my website. When other kids were bragging about how their dog could sit and roll over, I was bragging about my latest Betta Fish and the cool sea castle I just added to his aquarium. 

Jason aquariume

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