How to Raise KH in a Freshwater Aquarium

How to Raise KH in a Freshwater Aquarium

KH is an important water element for all kinds of ponds and aquariums. This article will discuss the various ways of raising KH in freshwater aquariums. But before we delve into this, you should first understand what is meant by KH.

What is KH?

As mentioned earlier on, KH is an important water element for all kinds of pods and aquariums. Even though it is different from pH, the two are quite closely related. In fact, KH is often tested after finding out that the pH of water has a problem. 

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KH is basically a degree of the water’s buffering capacity or its ability to resist any changes in pH. It is normally expressed as ppm (parts per million) of carbonate salts and hence its name carbonate hardness. High KH values normally accompany high pH readings; an acidic pH, for instance, is usually an outcome of low KH.

Without the correct KH, the pH of your water is most likely to be unstable or wrong. Simply put, it is hard to maintain the correct pH without first controlling the KH levels; the two actually go hand in hand.

Why is it so important to your freshwater aquarium?

Your aquarium is constantly producing acids. How? You might wonder. The fish living in your aquarium poop and this waste gets broken down into ammonia. The beneficial bacteria living in your filter (the ones that get introduced during tank cycling) convert this ammonia into nitrite, which then gets turned into nitrate.

Note that nitrate and nitrite are both acidic. And given that the two are continually being produced, your aquarium’s pH will drop over time. If your water’s KH is very low, there won’t be anything to neutralize the produced acids. This results in a dangerous fall in pH that might the water toxic for both plants and fish. This is definitely something that you’d want to avoid.

The ideal KH levels for your aquarium will completely depend on what you have stocked in it. There is no set value as the “best KH level for your freshwater tank.” The best value all depends on the species of fish that inhabit your tank.

How to test for the KH of your aquarium

It is important to know the exact KH level of your tank’s water. You can test for your water’s KH using special KH test kits. The good thing is that these aquarium test kits are not only affordable but also very easy to use. In addition, one test kit can be used to carry out hundreds of water tests. Just ensure that you carefully follow the listed instructions.

How to increase KH

You have tested your tank’s water and have found out that the KH levels are too low and need to be raised. Below are some of the ways that you could use to achieve this:

Changing your tank’s water

The water supply in your area might be of high KH. This means that conducting a simple water change automatically replenishes your freshwater tank’s KH levels. This is why it is advisable to not only test for your tank’s KH but also that of your tap water; it will offer you a better understanding regarding how to proceed with adjusting your aquarium’s KH if need be.

If your tap water KH is above 4 dKH (degrees of carbonate hardness and 1 dKH is equivalent to 17.9 ppm), a weekly 25 percent water change is enough to replenish the reduced KH.

You could also use that time to maintain your aquarium. You could get a nice gravel cleaner to suck out all the junk from your substrate. Doing this helps to prevent the build-up of nitrates that are known to cause a drop in KH levels.

Use of alkalinity buffers

Most aquarium brands also manufacture their own alkaline buffers. Different brands rely on different elements to raise KH; some depend on soda ash, others on baking soda, and others on phosphate- they are all effective when it comes to raising KH. The above elements are carefully mixed with other ingredients to come up with a final product that helps you achieve your anticipated KH.

In fact, beginners are mostly advised to use alkalinity buffers to raise KH over other methods as this eliminates any guesswork when adjusting your tank’s KH.

The best part is you can find alkalinity buffers that have been specially designed to match what you’ve stocked in your tank, in this case, freshwater. Some alkalinity buffers have even been designed for specific fish species, for instance, goldfish buffer, Arowana buffer. Tanganyika buffer, and discus buffer among others.

You should, however, stay away from phosphate-buffers by all means. Phosphates have been found to deplete certain essential minerals such as magnesium and calcium from your tank. In addition, high levels of phosphate result in the stunted growth of coral.

Introduction of stunted coral

Crushed coral can be obtained from dead coral reefs. Given that coral contains high levels of calcium carbonate, it can help to increase your aquarium’s KH.

You can either mix the crushed coral with a substrate or place it in a media bag and add it to your filter. Experts, however, recommend the second method (filter method). If crushed coral is added to gravel, it could compact after a while and start trapping uneaten food, fish waste as well as other gunk.

Remember that there is no need to constantly add crushed coral to your aquarium; you just leave it to rest there and do its magic!

How does it work?

Remember, your aquarium is constantly producing acids (from nitrates and nitrites). The crushed coral reacts with these acids to release carbonate and calcium to your tank water, thus raising its KH.

And how much should you introduce to your tank?

The quantity does not quite matter. Introducing a lot of crushed coral will only make it raise the KH levels faster. Given enough time, however, a smaller amount of coral will also eventually increase the water’s KH to the same level. The water equalizes. This is due to the fact that as pH increases, the water becomes more alkaline (less acidic) and the coral will not be capable of releasing as much carbonate and calcium.

Use of Aragonite

This is simply calcium carbonate’s crystal form. Similar to crushed coral, the acids in your tank water reach with aragonite to release carbonate and calcium.

However, different from crushed coral, this one (aragonite) is composed of small sand-like particles. And it is because of this that freshwater aquariums often utilize it as substrate sand.

Aragonite significantly raised KH and pH over time. It is thus mostly suitable for hard-water-loving creatures like African cichlids.

Beginners are not advised to use this method. If you find out that it is interfering with other water parameters, you will have to take out the entire substrate, which is a tedious and frustrating task once you’ve set up your aquarium.

Use of dolomite rock

Also known as dolostone, this is basically a calcareous rock that is composed of mainly magnesium, carbonate, and calcium. Once it reacts with the acids present in your aquarium water, it releases all of these three elements into the water, subsequently increasing the KH of your aquarium.

Dolomite releases less of these three elements at higher pH values. It is because of this reason that it is often utilized in freshwater tanks. The high pH in saltwater aquariums reduces its effectiveness. 

It is preferred by a lot of aquarium hobbyists because it’s available in a variety of colors, which makes it suitable for use as a substrate.

Use of baking soda

This is something that you can easily find. The amount of baking soda to be used depends on the size of your aquarium. For instance, adding a single teaspoon of baking soda to an aquarium with a capacity of 100 liters increases the dKH by 2 dKH.

Note that you should not add in a lot of baking soda at one go to increase KH as this sudden change could be toxic to your fish. Instead, add it in little by little, taking into consideration the size of your aquarium.

Also, ensure that what you are purchasing is baking soda and not baking powder; there is a huge difference between the two.


KH is among the most ignored as well as least understood aspects of aquarium water chemistry. As you’ve seen, KH plays an important role in ensuring that your aquarium’s parameters are kept stable.

Without KH, your tank’s pH would be unstable, stressing your aquarium’s plants and fish and resulting in all kinds of issues. And if you wish to make some adjustments to your pH, you first have to adjust the KH.

Its importance to the proper health and functioning of your aquarium’s inhabitants cannot be stressed enough.


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