How To Lower Gh In Aquarium [6 Easy Methods]

Hi, this is your friend Clifton Ervin, the founder and chief editor of this site, Aquariumwolf. I completed my graduation in marine biology and became...Read more

Lowering GH in aquariums is also known as softening the aquarium water. Since hard water can harm your fish, you should keep the tank clean to maintain a good GH. If the GH crosses 10, it indicates that you need to lower it. Now the question is: how to lower GH in aquarium?

Well, to lower GH in an aquarium, you can use a crystal water softener, lime-free gravel, distilled water, peat moss, etc., or you can use a reverse osmosis machine, which is the most expensive and reliable method.

Reverse osmosis machines produce deionized water. Since deionized water has reduced magnesium and calcium, you can use it to lower aquarium GH. A high GH indicates high calcium and other minerals, which can pollute the aquarium environment.

Now here in this article, we’ll show you how to lower GH in aquarium, so without further ado, let’s dive into the deep discussion.

Why Do You Need To Lower Aquarium General Hardness or GH?

Unless you have specific types of fish that need high GH to survive, such as goldfish, livebearers, or African cichlids, you must lower the GH of your aquarium. Following are the reasons why:

Why Do You Need To Lower Aquarium General Hardness or GH

Damages The Aquarium Ecosystem

Most fish cannot survive in a high GH environment. On top of that, aquatic plants are even more sensitive to high GH than fish. So it is always recommended to maintain an ideal GH of 4-8 in the aquarium.

Lowers Resistance to Diseases

If your aquarium has a GH of above 10 for a long time, it can hamper the fish by weakening their immunity. It is because an excessive amount of calcium and minerals is never good for fish health.

Imbalances Fish Hormones

A high GH can affect the ideal hormonal balance of the aquarium fish. It leads them to be less appetitive, sluggish, and even aggressive. If such behavior continues for a long time, it poses a threat to their very existence.

Aquarium GH Chart

What you keep in your aquarium will fully determine its optimal GH level. And for this reason, it is better to follow a table that enlists the ideal GH for different types of aquariums and fish tanks.

Types of Fish Aquariums Ideal GH Levels
Plant Aquarium 3-8 dGH
Discus Aquarium 3-8 dGH
Shrimp Aquarium 4-8 dGH
Tropical Fish Aquarium 4-12 dGH
Fish Pond 4-12 dGH
Axolotl Aquarium 7-14 dGH
Brackish Aquarium 12-20 dGH
African Cichlid Aquarium 12-20 dGH

How To Lower GH In Aquarium

Please remember that you only need to lower the GH in an aquarium for the following two reasons:

How To Lower GH In An Aquarium

  1. If the GH is above 10
  2. If you don’t have any fish that require high GH

Lowering it otherwise can reduce the calcium and magnesium in the aquarium, which can be fatal to the fish.

Method 1: Use Water-Softener Crystals

If you’re on a budget, use a crystal water softener to lower the GH in your aquarium. These substances are salt mixtures created specifically for aquarium usage. The best thing about this is you can buy it from anywhere.

A good water softener salt will cost you less than 10 USD. They can lower the GH in your aquarium by replacing calcium and magnesium with sodium.

For every 20 gallons of fish tank water, you must apply 1 liter of water softener crystals. You can easily calculate the amount needed based on this rule.

Method 2: Use Lime-Free Gravel

Having lime-free gravel in an aquarium is generally a good thing. These natural materials are great for maintaining a healthy environment for fish. Lime-free gravel is great for decreasing excess calcium and magnesium in aquarium water.

An important thing is you must use water filters in your aquarium if you have lime-free gravel. Otherwise, fish food and waste can accumulate under the gravel, polluting the water.

Method 3: Apply Distilled Water

Even though you can make distilled water at home, you will still need to buy it since this method will require a large amount. And a gallon of distilled water will cost you only a few dollars.

First, empty the aquarium water by at least half. Then pour distilled water to fill up the aquarium. It will lower the level of minerals, including calcium and magnesium, eventually reducing the GH level.

Method 4: Use Sphagnum

You can keep sphagnum in your aquarium only if it has no lime. Sphagnum is also famously known as peat moss. Just like lime-free gravels, peat mosses can also lower the calcium and magnesium rate, decreasing the aquarium GH.

However, this method only applies when your GH is not extremely high. If your GH is moderately high, you can use peat moss in your aquarium.

Method 5: Remove Existing Tap Water Stains

If you use tap water in your aquarium, it can sometimes create stains in the glass. These stains contain minerals such as calcium and magnesium. Cleaning the aquarium glass thoroughly can decrease the GH level as it removes the minerals.

Method 6: Use a Reverse Osmosis Machine

These machines are also known as domestic water softeners. Many people use this device to soften their drinking water. However, implementing this method is expensive. It can cost you nearly 200 USD or more.

And you only can opt for this method when you have a large fish tank. This process is continuous, meaning it will keep the water free from hardening materials such as calcium and magnesium all the time.

NB: Using Reverse Osmosis Machine can dramatically reduce the GH level of your aquarium, which is also not a good sign for your aquarium fishes.  So to maintain an ideal GH in your aquarium, you should buy products that increase the GH, such as crushed coral or crushed oyster shells. When your fish tank GH is lower than 4-5, you can apply some of these products by turning the machine off until GH increases unusually.


Sometimes, people confuse GH with pH. They are different things. Moreover, there are other concerns regarding aquarium GH, which we have come across in many online forums. The following are some of them:

Why Is My Aquarium GH High?

If your fish food is high in calcium and magnesium, it can increase the aquarium’s GH. Plus, a natural supply of minerals tends to release a variety of ions when added, which influences various water parameters.

Do Almond Leaves Lower Aquarium GH?

Yes, almond leaves are one of the methods with which you can lower the level of GH in your aquarium. Dried-up almond leaves can soak water hardeners, such as minerals, calcium, and magnesium. So using some of it in a fish tank can reduce its GH.

Is Low Aquarium GH Good For Fish?

Whether low GH is good for your fish tank depends on the kinds of organisms you have. You must preserve a low GH if your aquarium is plant-heavy in quantity. And, some fish such as discus or other soft water fish.

What Does High GH Mean In A Fish Tank?

Water that has a low GH is thought to be softer than water. So, water with high GH means harder. As a result, the calcium and magnesium content in soft water aquariums are very low or absent, and vice-versa.


While regularly cleaning the aquarium water is the easiest way to maintain a low GH, there are some easy ways. But whatever method you follow, measure the GH with a test kit beforehand.

And know about the types of fish you have before attempting to lower the aquarium GH. If your fish needs high GH to survive, there is no need to lower it unless it is exceptionally high.

Even though most aquatic enthusiasts would say that buying a domestic water softener is the best way to lower GH, it is not true if your aquarium is small or the fish do not need very low GH to survive.

Hi, this is your friend Clifton Ervin, the founder and chief editor of this site, Aquariumwolf. I completed my graduation in marine biology and became an Ichthyologist. One of my favorite hobbies is aquarium keeping; therefore, I love to talk about fish keeping, breeding, food behavior, etc., and much more relevant to aquarium maintenance. I have created this site Aquariumwolf, to share my 20 years+ of experience and knowledge with all new to this journey.

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