5 Ways To Raise KH In Aquarium

Last Updated on 2023-05-24

The carbonate hardness or KH of the water is one of the most important water parameters you should test and monitor, especially if you’re new to fishkeeping and have recently set up an aquarium. 

You can raise the KH in your aquarium by changing the water. You can also use alkalinity buffers, crushed coral, aragonite chips, and pieces of Dolomite.

Read on to learn more about raising KH in your aquarium and find out why it is an important water parameter. Also, discover some probable reasons why the KH in your aquarium might be low. Happy reading!

How To Raise KH In An Aquarium (The Short Answer)

Raising KH in your aquarium is vital for keeping your fish happy and healthy. And fortunately if you want to raise the KH, it’s not a difficult process.

To raise the KH in your aquarium use alkalinity buffers, crushed coral and other forms of calcium carbonate, aragonite, and dolomite. And lastly you can perform a water change and add tap water with a high alkalinity.

Doing all of the following is a great way to raise the KH!

What Is Aquarium KH?

KH refers to the carbonate hardness of the water. In fishkeeping, it is one of the most important water parameters to monitor and test on a regular basis. Carbonate hardness measures the amount of carbonates and bicarbonates that are present in the aquarium’s water. A high or low KH isn’t good for fish and aquatic plants, and it must be brought to normal in order for marine life to thrive. KH also helps maintain the pH of the water and prevents it from falling to dangerously low levels that can be harmful to the fish.

What Is The Difference Between KH And GH?

There are two types of water hardness that everybody who is setting up an aquarium should be aware of. KH, as we discussed before, refers to how much carbonates and bicarbonates are there in the water and plays an important role in maintaining the pH. GH, on the other hand, is the general hardness of the water. It is a measure of the metal ions present in the water, particularly calcium and magnesium ions.

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Why Is KH Important To Your Aquarium?

KH plays an important role in maintaining optimum water conditions in your aquarium. Here are a few reasons why it is important.

1. Prevents the Water From Becoming Too Acidic

The carbonate hardness (KH) prevents the water in the aquarium from becoming too acidic. It increases the pH of the water and makes it more resistant to fluctuations in the pH level whenever any acid is added. Since acids are constantly produced in the aquarium by the beneficial bacteria, high KH levels will ensure that those acids don’t lower the pH to dangerously low levels. So, a certain range of KH levels is needed to maintain an optimum pH level in the tank.

2. Prevents Fish From Dying

Fish are extremely sensitive creatures and need optimum water conditions to survive. Maintaining the correct pH level is an important part of ensuring water conditions are ideal. Although most fish can survive in a range of pH levels, highly acidic conditions might prove to be fatal for some species. Besides killing fish, acidic water can also cause them to become sick and can stunt their growth as well. To prevent this and to ensure your fish thrive in the water, it is important to have a certain level of KH in the tank.

3. Restricts Algae Growth

Algae are known to grow and thrive in mildly acidic water conditions, especially if they’re receiving a good amount of light. Widespread algae growth in your aquarium is often an indicator of a low pH level as well as low KH. Having a lot of algae in the tank due to low pH is not good for the fish. The algae can spread all over the tank, making it difficult for the fish to swim around.

4. Fish Can Get Stressed in Acidic Water

As we previously mentioned, fish are quite sensitive creatures, and less than optimum water conditions are likely to make them stressed. Since they only thrive in certain pH conditions, a low pH can make them stressed and eager to escape the tank. This can also affect their diet, growth, and movement. Thus, if your fish appear to be stressed, one of the reasons for that can be low pH and low KH levels in the tank.

5. Fish Can Develop Health Problems

Besides dying, fish can also develop certain health problems if the water in the aquarium becomes too acidic. Acidic water can decrease their appetite, slow their metabolic processes, and make them appear pale and sick. These symptoms are their bodies’ responses to the acidic conditions to avoid nutritional starvation. In some species, these symptoms may not be worrying and can be an indication that the fish are trying to adapt to the new conditions. Once the pH returns to normal, the fish will recover.

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How To Test And Measure KH In An Aquarium

Here, we mention some methods and tips to test and measure KH in your aquarium. Keep reading!

1. Use Strip Tests

Using strip tests to test and measure the KH in your aquarium is an easy and effective way. Separate strip test kits are available for testing the KH and GH in your aquarium. Do keep in mind that you cannot test both types of water hardness using only one strip. So, how do you test the KH using a strip test? Take a small sample of water from your aquarium in a separate cup and dip the strip in it. Observe the color change in the strip and refer to the color chart to see the corresponding KH level for that color.

2. Use Reagent Tests

Reagent tests work in a similar fashion to strip tests. Reagent test kits usually consist of a chemical reagent and a color chart that indicates the KH levels for various colors. Again, you take a small water sample from your aquarium and add a few drops of the reagent to it, as per the instruction manual in the kit. Once the color changes, you can see what KH level it corresponds to in the chart.

3. Take a Water Sample to a Local Fish Store

If you don’t have a strip test kit or a reagent test kit, you can simply take a small sample of your aquarium’s water to your local pet store or fish store. They can do the test for you using that sample and can give you a detailed analysis of the water conditions. This way, you can not only get the KH levels tested, but also the GH, pH, and other water parameters. Fish stores usually charge a small fee for their services, but some might even do it for free!

4. Test KH Levels Regularly

To ensure the water conditions in your aquarium remain optimum at all times, you should make a habit of regularly testing the KH, among other water parameters. You can do this as part of your regular aquarium maintenance and cleaning routine. If you’ve recently set up an aquarium and are keeping fish for the first time, it is a good idea to monitor your KH and GH levels daily. Once your aquarium’s ecosystem is established, you can reduce the frequency of your tests.

5. Look Out for Low KH Signs

It can be hard to determine if the KH in your aquarium is low without performing tests. But there are certain signs you can look out for that indicate the water has a low KH. First, you might notice your fish are becoming stressed. While this can happen for a variety of reasons, persisting acidic water conditions is a key one. Other signs include sudden algae growth, fish becoming pale, and some even dying.

What Is The Best KH Level For Your Tank?

KH is one of the most important water parameters, and it must be maintained at an optimum level in order for the fish and aquatic plants in your aquarium to thrive. So, what is the best KH level for your tank? The answer: between 4 and 6 dKH (degrees of carbonate hardness) for freshwater fish tanks. For saltwater fish tanks, the range is a bit higher, from 5 to 8.5 dKH. If your fish tank has a KH value that lies in these ranges, then you have nothing to worry about!

Why Would You Need To Raise KH In An Aquarium?

In certain cases, raising the KH of the water in your aquarium is important and necessary. The reason behind this is that a higher KH level that falls in the ranges mentioned above gives the water an increased buffering capacity. This means that the water is less prone to fluctuations in the pH since any acids that are released will be neutralized by the carbonates. This ensures that the pH remains at the optimum level and that your fish thrive.

How To Increase KH In Aquarium

If the KH of your aquarium’s water is low, here are a few things you can do to increase it.

1. Replace the Water

Simply changing the water in your aquarium can replenish its KH. Tap water in the US often has a high enough KH to increase the KH in your aquarium. Before replacing the water in your aquarium, carry out a test to determine if you need to increase the KH. If the KH is low, you can replace about a third or a fourth of the tank water with tap water once every week or once every two weeks.

2. Use Alkalinity Buffers

Another method to increase the KH in your aquarium is to use alkalinity buffers. Most alkalinity buffers available normally contain baking soda or phosphate that do a good job of raising the KH levels in your aquarium. Using these buffers is better than using the ingredients they contain separately, as these are more effective and consistent. Moreover, alkalinity buffers are available for freshwater and saltwater tanks, and some are even designed for certain fish species.

3. Use Crushed Coral 

In case you don’t have alkalinity buffers to increase the KH in your aquarium, you can use crushed coral to do the job. The reason crushed coral is so effective in increasing the KH is that it contains a lot of calcium carbonate, which works very well in raising the KH and lowering the pH. To put it in your tank, you can either mixed with the tank’s gravel, or you can seal it in a bag and add it to the filter.

4. Use Aragonite

Another substance you can use to raise the KH of your tank is Aragonite. Aragonite is actually the crystal form of calcium carbonate. It is also commonly used as a substrate in aquariums. Besides increasing the KH, it can also increase the GH and the pH. However, Aragonite must be used with caution since it has the potential to disturb the water parameters, and removing it will be a difficult task if it’s mixed with the gravel.

5. Use Dolomite

Dolomite is a mineral compound containing calcium magnesium carbonate. If you put it inside your aquarium, it does an excellent job of raising the KH of the water as it releases calcium and magnesium. It raises not only the KH but also the GH and the pH. Dolomite is commonly used as a substrate in freshwater aquariums since saltwater greatly reduces its efficacy.

Why Is My KH Low In My Aquarium?

There can be several reasons your aquarium has a low KH. Here, we list down some of the most important and common reasons for that. It is important to diagnose the reason correctly and then act accordingly.

1. Not Changing the Water Regularly

One of the most common reasons for low KH in your aquarium might be not changing the water regularly. KH levels in the water reduce with time as waste is converted into nitrites, nitrates, and ammonia. So, the KH needs to be replenished regularly, and that can be done by replacing some of the water in the tank. This is something that needs to be done on a frequent basis, and many beginners make the mistake of not changing the water as often as they should. This can cause the KH to drop and the water to become acidic.

2. Overcrowded Aquarium

Having an overcrowded aquarium can create a host of problems and make the water conditions unsuitable for every fish and aquatic plant. One of the consequences of having an overcrowded aquarium is quickly depleting KH in the water. If there are a lot of fish, they produce a lot of waste, and the carbonates in the water are not enough to convert them into ammonia, nitrites, and nitrates. This can make the water acidic very quickly.

3. Lots of Carbon Dioxide in the Aquarium

Carbon dioxide is a necessary requirement of aquatic plants, but having too much of it in the aquarium can adversely affect the water’s carbonate hardness. The problem with having too much CO2 in the water is that it can dissolve into carbonic acid. If carbonic acid isn’t used up by the aquatic plants, it can easily lower the KH as well as the pH.

4. Accumulation of Waste in the Aquarium

This problem is somewhat similar to overcrowding, which we discussed earlier. Like all living creatures, fish produce waste. But if there’s too much waste in the aquarium, either due to overcrowding or some other problem in the water, it can adversely impact the KH in the water, lowering it and making the water acidic. If there’s a lot of waste, then the carbonates in the water aren’t enough to convert it into nitrate, nitrites, and ammonia. This accumulation of unconverted fish waste can turn the water acidic.

5. Addition of Chemicals and Acidic Substances

If your aquarium has none of the four problems we mentioned previously, but still the KH of the water is low, then a reason for that might be the addition of acidic substances to the tank water. Beginners and those who’re keeping fish for the first time might add certain chemicals intending to improve the quality of the water. If this is done without proper knowledge of the impact of adding that chemical, it can potentially lower the KH of the water and make it acidic.

How To Decrease KH In Aquarium

So, now you know the reasons why your aquarium’s water has a low carbonate hardness, and you’ve also read about ways to increase it. But sometimes, having a high KH is also not good for your aquarium since it can increase the pH way beyond the optimum range. So, how do you decrease the KH in your aquarium?

1. Put Acid Buffers Into the Aquarium

Just like alkalinity buffers raise the KH of the water, acid buffers lower it. They work by converting excess carbonates into carbon dioxide. This reduces the KH, which in turn reduces the pH. Acid buffers work best in aquariums that have aquatic plants since they can remove any excess carbon dioxide that is produced. Adding acid buffers to tanks that don’t have plants can drastically reduce the pH, turning the water acidic.

2. Add Some Distilled Water

Distilled water is a special kind of water that has been processed to remove impurities. It can be used to lower the KH in your aquarium by adding it to the water. If you want to have some carbonates in the water, mix the distilled water with some tap water before adding it to your aquarium. Distilled water works perfectly for smaller tanks.

3. Perform Reverse Osmosis (RO)

Reverse osmosis is a process that is used to purify water by passing it through a semi-permeable membrane. The membrane filters out all the impurities, and the water that is left is pure. If you want to add pure water with no carbonates to your aquarium to lower its KH, then investing in a reverse osmosis system might be a good idea. 

4. Use Indian Almond Leaf

Indian almond leaves are leaves that are grown on the Terminalia catappa tree. They can be added to your aquarium if you want to lower the water’s KH. They work by breaking down and releasing tannic acid, which neutralizes the excess carbonates in the water. These leaves work best if your KH and pH are moderately high and are not very effective if the pH of the water is too high.

5. Use Peat Moss

One last solution you might want to explore for lowering the KH in your aquarium is to use peat moss. Peat moss works as Indian almond leaves do. It releases tannic acid, which neutralizes the excess carbonates and lowers the KH. Once again, it doesn’t work well if the pH of the water is very high.


Here are some frequently asked questions that people have about raising the KH in their fish tank.

How Do You Raise KH Without Raising pH?

If the KH in the water rises too much, it can also start increasing the pH of the water. This is because KH is linked to pH, and increasing it will also increase the pH. You can increase the KH without increasing the pH by putting Aragonite in the aquarium’s filter when the pH starts falling below 6.5. Check out this article for more detailed instructions regarding this.

Does Baking Soda Raise KH?

Yes, baking soda can be used to raise the KH of the water. Baking soda contains sodium bicarbonate, which helps raise the KH without raising the pH too much. Adding baking soda also doesn’t increase the general hardness (GH). Have a look at this guide for more details about adding baking soda to increase KH.

Is KH The Same As Alkalinity?

Yes, the carbonate hardness (KH) of the water is the same as its alkalinity. KH is a term used to express the alkalinity of water in degrees of carbonate hardness (dKH) or ppm. One dKH equals 17.9 ppm. Have a look at this guide, as it offers a detailed overview of KH and alkalinity and explains how they’re linked.

Will Increasing Kh Raise pH?

KH and pH go hand in hand because KH helps keep pH levels from changing too quickly. In fish tanks, pH levels can drop, but increasing KH will neutralize more acid, which will help keep the pH levels from getting too low.

Why Should You Avoid 0 Kh In Your Aquarium?

Zero KH is super dangerous because it can make the pH level drop too low. That’s terrible news for the fish and plants living in the tank.

Is High Kh Bad For Fish?

A high KH usually won’t hurt your fish because it helps keep the water stable and prevents pH from changing too much. But if the KH gets super high (above 20 dKH), the water can become too rigid and alkaline, which might not be suitable for some fish species. So, research your fish and keep the water conditions in check!

How Much Baking Soda Is To Raise KH?

Adding a teaspoon of sodium bicarbonate to 50 liters of water will increase the KH by around four dH. The sodium bicarbonate also helps bring the pH level to a stable point of about 8.2.


There’s no doubt KH is one of the most important water parameters that must be kept at an optimal level to ensure your fish thrive well. In this guide, we talked about the importance of KH and the importance of testing and monitoring it. We also put forth ways to increase or decrease the KH in your aquarium.

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