How to Raise KH in an Aquarium

planted aquarium with fish

Aquariums are a beautiful addition to any home. With the proper care, it can be a fun and rewarding hobby. Keeping your aquarium healthy involves maintaining the proper levels of KH, or carbonate hardness. In this article, you will learn how to raise KH in your aquarium so that your fish and aquatic plants can thrive.

planted aquarium with fish

How do you increase KH?

If you want to raise the KH in your aquarium, you can do a few things. See the table below for some ideas. 

Add baking soda to the water. Add crushed corals to the aquarium.
Pro: This method raises the KH quickly. Pro: Crushed coral can help to stabilize the pH.
Con: It will also increase the pH.Con: This method raises the KH at a slower level, avoiding any problems with raising it too fast. 
Tip: If you do this, use caution and only add small amounts at a time. Tip: The lower the pH in the tank, the faster the coral will dissolve. Pay attention to this as you add it in. 

What is aquarium KH?

Aquarium KH, or carbonate hardness, measures the dissolved carbonates in your aquarium water. Carbonates are a primary component of many aquarium substrates and play an essential role in buffering pH. Aquarium KH can be increased by adding crushed coral, limestone, or dolomite to your aquarium. 

GH, a similar component, measures the general hardness in the tank. When you want to measure your GH, all you have to do is look at the calcium and magnesium ion levels in your tank. While GH won’t impact your ability to grow aquatic plants, it does affect how your fish can live. 

How can KH affect plant growth in freshwater aquariums?

KH has no innate value to most plants. Some plants can use carbonates as a carbon source and will grow better in higher KH water when deprived of other carbon sources.

However, this is very energy intensive for the plant, as it has to extract carbon from carbonates rather than CO2. Its sole purpose for plants, if any, is as a buffer to prevent tank water from getting overly acidic. Bacteria consume it in small amounts as part of the ammonia oxidation process.

As we know, KH directly relates to pH because it prevents the tank’s pH from changing as quickly.

In aquariums, pH levels tend to drop over time. So, when KH is raised, more acid is neutralized and pH tends to stay higher. For instance, it can be observed that if you have a higher pH of 8.0 and a buffering agent like crushed coral is added, KH will rise but the pH value doesn’t move as much. However, if you have a lower pH and add crushed coral, both pH and KH values tend to increase.

KH measures the amount of carbonates and bicarbonates in water, which affects the buffering capacity of the water. This means that KH helps neutralize acids and prevents your pH from changing too rapidly, which is useful because sudden pH crashes can cause health issues in your plants and fish.

Low KH means your water has less buffering capacity and the pH swings easily. High KH means the tank water has the more buffering capacity and the pH level is hard to change.

How do you measure KH in an aquarium?

There are a few different ways to measure KH in your aquarium.

The most accurate way is to use a test kit you can purchase from a pet store or online. Test kits usually come with a dropper and a vial of liquid reagent. To use the kit, you’ll add a few drops of the reagent to a sample of your aquarium water and compare the color of the water to the chart included in the kit. This will give you a reading in degrees KH.

You can also use a pH test strip to get a rough idea of your KH levels. Simply dip the strip in your aquarium water and compare the color change to the chart on the packaging. This method is less accurate than using a test kit, but it can still give you a good idea of where your KH levels are at.

What is the best KH level for your aquarium?

There is no definitive answer to what the best KH level is for your aquarium. However, many experts recommend keeping KH levels between 30 and 40 ppm. This range will provide sufficient carbonate hardness for most aquarium plants and animals.

Some aquarium hobbyists believe that raising KH levels can help to buffer against pH fluctuations. This is because carbonate hardness helps to stabilize pH levels in the water. Therefore, if your aquarium experiences sudden pH changes, raising KH may help to mitigate these fluctuations.

How do you maintain KH and pH in an aquarium?

pH is a measure of how acidic or basic the water is, with 7 being neutral. Alkalinity is a measure of how much carbonate and bicarbonate are present in the water, which helps to buffer the pH and keep it from fluctuating too much. While it is possible to raise KH without raising the pH, you have to be careful.

In freshwater tanks, it is common for the KH to drop when:

Maintaining proper pH and alkalinity levels can be challenging, but it’s important for the health of your fish and other aquatic creatures. Testing the KH and pH levels (using a test kit) in your tank regularly is an important part of owning an aquarium. If it is below 4, you’ll need to raise it. You can do this by following the aforementioned tips or adding a commercial product designed to raise KH. 


If your aquarium’s KH is too low, raising your aquarium KH can be as easy as adding some baking soda. It is recommended that you stick to a KH of around 30 to 40 ppm. When making changes to your aquarium, you should regularly test the water for KH drops. Maintaining the KH in your aquarium is essential to having a healthy ecosystem for plants and fish.


Aquarium Water Quality: Total Alkalinity and Hardness

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