How To Lower gh in Aquarium

In-depth knowledge of Gh or General Hardness is essential for owning an aquarium. Yet most aquarium owners are clueless and do not take this aspect seriously. Some do not even know why it should be taken seriously.

The Gh level of your aquarium plays a vital role in keeping your fish in the best condition. It measures calcium hardness, magnesium, and carbonate hardness. 

Moreover, it is also inclusive when covering aspects like your aquarium KH and PH. If you didn’t know, there is a specific level of Gh that is appropriate for your fish.

How To Lower gh in Aquarium

In this article, you will learn all you need to know about Gh and how to lower Gh in aquarium which is suitable for your fish if you have noticed the Gh in your aquarium is high.  

To begin with, what do you understand by General Hardness (Gh)

What General Hardness (Gh) Really Means

GH basically measures the total concentration of magnesium compounds and calcium, which are essential for your fish to survive. The correct General Hardness (Gh) level for your aquarium is essential for the survival of your fish.

For instance, freshwater fishes will survive in an aquarium with a Gh of 6-degree to 12-degree Gh like the African Cichlids. In contrast, fishes like South American Cichlids would survive in much softer water or lesser degree Gh, ranging from 3-degree Gh to 5-degree Gh.

Nevertheless, before you choose any species of fish for your aquarium, do the necessary research that would help you decide the type of fish that can survive in the current aquarium Gh that you have.

If you have a particular fish you like to keep, and your aquarium Gh is too high, you can efficiently and effectively reduce the Gh of your aquarium and provide your fish with a suitable environment.

A lot of damage could be done to your fish if you keep them in an aquarium with a high Gh, but what are the effects, and why should you reduce it.

Why You Should Lower the Gh in Your Aquarium

If your aquarium water has a General Hardness higher than 12-degree, it would be difficult for your fish to survive. Hence you have to work towards reducing your aquarium Gh. 

However, there are other reasons why you should lower the Gh in your aquarium, which should help you take this aspect of owning an aquarium seriously.

1. Helps to build your fish’s resistance to diseases

If your aquarium has a high level of Gh, this would affect your fish’s immune system. And it can make it difficult for them to fight against an illness that usually shouldn’t be too difficult for them to recover from, eventually causing your fish to swim slowly and look sickly.

2. Increases your fish’s chances of Surviving

A high level of Gh in your aquarium would reduce the survival rates of your fish. It can also cause them stress and loss of appetite, obviously reducing their chances of surviving. How can your fish survive if they are constantly restless and don’t eat?

3. Reduces aggression

The Gh level of your aquarium can affect the mood of your fish. Lower Gh in your aquarium makes your fish calmer and less aggressive. In contrast, high Gh in your aquarium would do otherwise.

The aggression caused by high Gh results from your fish not being able to relax and get used to the environment. This makes them act out and try to release their frustration on the next available victim, usually smaller fish.

What Should Be the Best Gh for Your Aquarium?

This can be a tricky question, but it is not one without an answer. The best Gh for your aquarium is dependent on what type of fish you keep or intend to keep in your tank.

But first, is the General hardness of your aquarium measured? Gj is usually measured in part per million (PPM) or degrees of general hardness (dGH), and 1 dGH is about 17.9 PPM. So don’t get confused when you see terms like this.

Here are some guidelines you can follow to make the best decisions.

African Cichlid Tank12-20 dGH
Axolotl Tank7-14 dGH
Brackish Tank12-20 dGH
Discus Tank3-8 dGH
Pond4-12 dGH
Shrimp Tank4-8 dGH
Tropical Fish Tank4-12 dGH

What Should You Use to Test the GH of Your Aquarium?

The best way to test the Gh level of your aquarium is to use an aquarium test kit. The aquarium test kit would give you your result either in dGH or PPM, depending on the type you are using. And there are many affordable aquarium test kits that are easy to use and give you accurate results.   

You can also try aquarium test strips which can sometimes give you a more accurate result than liquid test kits. Testing the Gh of your aquarium is very important, especially if you want to keep sensitive fish or fishes that have been identified to only survive in either hard or soft water.

8 Ways That Shows How To Lower GH In Aquarium

Now that you have a better understanding of what Gh means and why it is vital for the survival of your fish. Taking suitable measures in order to reduce the high level of the Gh in your aquarium should be your next move.

Here are several methods you can choose from to achieve the best result for you and your fish.

1. Use water softening pillows with your aquarium filter

Using a water softening pillow is one the most effective ways to lower the Gh in your aquarium. The water softening pillow contains resin beads that bind and limit minerals like magnesium and calcium from entering the water.

The pillow removes calcium and other minerals, thereby reducing the hardness of the water. Use the pillow with your aquarium filter either by attaching it to the filter with zip ties, hose clamps, or stuffing it into the water inlet of the filter. This would ensure that the water flows through the filter into the aquarium.   

2. Change the water you use in your aquarium

Suppose you are going to use this method. In that case, you have to do so carefully and understand the chemistry involved in different water interactions that can happen in your aquarium. 

Regardless, changing your aquarium water is also an excellent way to reduce The Gh of your aquarium. There are also various options under this;

  • Use water that you are sure has low Gh and would be safe for your fish.
  • Consider reverse osmosis, which means you would need to get a RO/DI device that would help you remove magnesium and other minerals, giving you pure water of about 99%  
  • Distilled water from a pet store would also be effective
  • Deionized water can be used too; it replaces ionized minerals that cause high Gh in water.
  • Tap water and drinking water are generally not good when using this method. Tap water hardness is too high and would not work effectively for reducing Gh in your aquarium.

3. Try water softening crystals

Another great method to consider is using water softening crystals. This method happens to be one of the cheapest and quickest ways to reduce Gh in your aquarium.

How it works is pretty simple, the crystal replaces magnesium and calcium with sodium ions which automatically reduces the hardness of the water. Sodium creates a balance in the mineral found in the aquarium water. It reduces the level of minerals that causes water hardness in your aquarium.

Water softening crystals is a chemical product and would usually come with instructions on how to use them in your aquarium. Follow these instructions closely so that you do not do more harm than good to your aquarium. For instance, you are expected to only use one liter of softening crystals every 20 gallons.  

4. Frequently Change Your Aquarium Water

This is another easy and safe way to reduce the Gh level in your aquarium. This method also does more than just reduce the Gh. It helps you get rid of fish waste, rotten plants, old food, and other debris.

You can replace the water in your aquarium with soft water that your fish can survive in. Use 25% of the water in your aquarium with a GH of less than 4. 

Do this until you get the right level. Note that this can take a few days, and ensure you do it gradually and use an aquarium test kit to ensure the GH level is suitable for your fish.

5. Buy Domestic Water Softeners for your Aquarium

There are some more affordable methods here, but if you want an effective and safe method for reducing the level of GH in your aquarium, then buy a Domestic Water softener.

This machine takes the water you would like to add to your aquarium through a resin tank. It takes away carbonate, calcium, and magnesium and replaces the carbonate with sodium ions which reduce the Level of Gh in the water.

6. Clean up Tap Water Stains

Water stains from when you fill up a container with tap water and leave it open for days. If you plan to use that same water as a replacement for your aquarium water. Hold up, here are some things you need to know.

Leaving tap water open in a container for days causes calcium to build upon the container walls and, without a doubt, increases the Gh level of the water. So you have to correct this before you use it.

There are two ways to do this

  • Use Calcium, Lime & Rust Remover (CLR)
  • Use Hydrogen Peroxide (3%)

Use either of these in the water for at least 5 to 30 minutes. It would remove the water stain.

7. Try Lime-Free Gravel

Using lime-free gravel is a great choice as they are chemical-free and great for aquariums. It is well-known that limestone builds up calcium and magnesium over time. 

Moreover, it only makes sense to try Lime-free gravel for the opposite result. Use them as the substrate for your aquarium. You can also use inert substrates like river rocks and crushed granite.

8. Use Peat Moss

Using Peat moss in your aquarium would also lower the Gh level of your aquarium. Ensure that the peat moss you would be using is free from lime and dolomite. Still, you have nothing to worry about as most of the peat moss sold is safe and would effectively reduce the Gh level of your water.


One thing is sure you can never say you don’t know how to reduce the water hardness of your aquarium after going through this article. Several methods have been made available to you. 

A well-detailed explanation of what GH means and how it affects your fish has been provided. Carefully follow them to ensure that you have a happy and healthy fish. 

Go on and share this with as many that might need it.

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