What is the difference between pH, gH and kH in Aquariums?

PH, Gh, and Kh are some of the commonly used terms in water chemistry. These terms also have a close relation with fish keeping and aquariums.

Check PH, Gh, and Kh values over time to ensure the existence and growth of fish. If you are active in fishkeeping or fish farming activities, then you might have heard about these terms.

The PH, Gh, and Kh values have a lot of importance in fish farming. But there are only a few people who know the importance of these values and maintain water accordingly. Most people only know about the PH of water.

If you are a fish keeper or have a related business, then you should know what Gh, Kh and PH values are, their significance, and how to maintain them in water over time. So in this post, I will explain what PH, Kh, and Gh values are and their significance.

Full forms of PH, GH, and KH

  • PH – PH stands for Power of Hydrogen.
  • Gh – Gh stands for General Hardness.
  • Kh – Kh stands for Carbonate Hardness.

What is pH and how it is measured?

Ph value in fishkeeping indicates the value of hydrogen ions present in the water. Checking the Ph value helps you understand the acidity or the alkaline presence in the water.

The PH value of water is measured using the PH scale which measures from values 1 to 14. When you get a measurement value near zero, it indicates that the water is very acidic. When the value is near 14, then it tells that the water is very alkaline. Also, values close to 7 indicate that the water is neutral.

See more Aquarium Tips

What is the required Ph range for Fish Farming?

Now let us check out the PH value range suitable for fish farming.

In general, the PH value from 6.5 to 8 is considered suitable for the majority of freshwater fishes. If you are a fish keeper, then you should maintain the required PH value for the well-being of the fish.

difference between pH, gH and kH

Preferred pH value for common freshwater fishes:

List of suitable pH ranges for various freshwater fishes.

Name of the Fish Required pH Range
Angelfish 6.5 to 7.0
Goldfish 7.0 to 7.5
Neon Tetra 5.8 to 6.2
Clown Loach 6.0 to 6.5
Silver Dollar 6.0 to 7.0
Hachetfish 6.0 to 7.0
Zebra Danio 6.5 to 7.0
Tiger Barb 6.0 to 6.5
Plecostomus 5.0 to 7.0
Harlequin Rasbora 6.0 to 6.5

Why should you maintain the required Ph level for water?

As I already said, it is very important to maintain the water with the required level of Ph for the well-being of fishes in it.

When the pH value of water goes less than 6.5, the acidity of water will increase and as a result, it will negatively affect the existence of the fish. And, when the pH value of the water goes higher than 8, the water will become more alkaline. This situation will cause difficulties for the fish to survive in the water.

What is Kh – Importance of Alkalinity in Aquaculture?

Kh (Carbonate Hardness) is the measure of carbonates and bicarbonates present in the water. Kh is also known as the ‘alkalinity of water’. It operates as a buffering system in the water.

Having the required Kh value helps to detoxify the presence of acids in the water and to protect water from the changes in Ph value. The changes in Ph value can lead to several health issues in the fish. Therefore, the Kh value is often checked in fish farming.

If the alkalinity is low, it indicates that the buffering capacity of water is less and the Ph value can vary faster. And, higher alkalinity (or Kh) indicates that the buffering capacity of water is high.

The Kh value of water is generally measured in dKH (Degrees of Carbonate Hardness) or PPM (Parts per Million).

1 dKH = 17.9 PPM

For example, 10 dKH to PPM = 10 * 17.9 = 179 PPM.

What is the suitable Kh range for Fish Farming?

The suitable Kh value range for freshwater fish farming is 70 to 150 PPM. For aquaponics fish farming, the recommended Kh value is 150 PPM, and, for bio floc fish farming the recommended Kh value is 200 PPM.

There are several test kits available to measure the Kh or carbonate hardness of the water. You can easily measure the Kh value and check if it falls under the required range.

What is Gh?

Gh (General Hardness) is the measure of Calcium and Magnesium ions present in the water. In other words, it measures the hardness of the water.

It is the easiest way to check if the water used for fish farming contains enough amount of salt and minerals.

Now let us check out the preferred Gh range for fish farming.

Suitable Gh range for Fish Farming

Gh value of water is measured in the same units that are used for measuring Kh, i.e. dKH or PPM.

The required Gh value will vary depending on the type of fish. For fishes like Tilapia, it is recommended to maintain a Gh value between 70 to 150 PPM.

Fish Preferred Gh Range
Tilapia 70 to 150 PPM
Betta Fish 70 to 300 PPM
Tropical Fish 70 to 140 PPM
African Cichlid < 50 PPM
Soft water fishes < 50 PPM

Ideal GH Level for Aquariums

GH (in dGH) GH (in PPM) Water Hardness
0 to 4 dGH 0 to 70 PPM Very soft
4 to 8 dGH 70 to 140 PPM Soft
8 to 12 dGH 140 to 210 PPM Moderately hard
12 to 18 dGH 210 to 320 PPM Hard
18 to 30 dGH 320 to 530 PPM Very Hard


How to increase Gh and Kh values in a Fish Tank?

Limestones and Dolomites can be used to increase Gh and Kh values of the water in fish tanks. Limestones are rich in Calcium Carbonate and, Dolomites are rich in Calcium and Magnesium.

What is the preferred Gh range for soft water fishes?

For soft water fishes, it is preferred to maintain the Gh value of less than 50 PPM.

How do I lower the GH in my aquarium?

To lower the GH value in your aquarium, you can introduce tap water into it if it is of low GH. Another way is to slowly introduce RO (Reverse Osmosis) water in the upcoming water changes.

What is the ideal KH level for a freshwater aquarium?

The ideal KH level for freshwater aquariums is between 4-8 dKH (or 70-140 ppm). But, it also depends upon the type of fish that you accommodate in the fish tank.


Aquarium Chemistry / Water Parameters

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