Difference between pH, gH and kH

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.

PH, Gh and Kh values should be checked over time for the existence and growth of fishes. If you are active in fish keeping 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 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 Scale Measurement
Ph Scale

Ph value in fish keeping indicates the value of hydrogen ions present in the water. Checking 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 to zero, it indicates that the water is very acidic. When the value is near to 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 as suitable for the majority of freshwater fishes. If you are a fish keeper, then you should maintain the required PH value for the good being of the fishes.

Preferred pH value for common freshwater fishes:

List of suitable pH range for various freshwater fishes.

Name of the FishRequired pH Range
Angelfish6.5 to 7.0
Goldfish7.0 to 7.5
Neon Tetra5.8 to 6.2
Clown Loach6.0 to 6.5
Silver Dollar6.0 to 7.0
Hachetfish6.0 to 7.0
Zebra Danio6.5 to 7.0
Tiger Barb6.0 to 6.5
Plecostomus5.0 to 7.0
Harlequin Rasbora6.0 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 fishes. 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 fishes 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 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 fishes. Therefore, 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 biofloc fish farming the recommended Kh value is 200 PPM.

There are several test kits available to measure the Kh, or carbonate hardness of 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 upon the type of fish. For fishes like Tilapia, it is recommended to maintain a Gh value between 70 to 150 PPM.

FishPreferred Gh Range
Tilapia70 to 150 PPM
Betta Fish70 to 300 PPM
Tropical Fish70 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 dGH0 to 70 PPMVery soft
4 to 8 dGH70 to 140 PPMSoft
8 to 12 dGH140 to 210 PPMModerately hard
12 to 18 dGH210 to 320 PPMHard
18 to 30 dGH320 to 530 PPMVery Hard

FAQs

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 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 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 fishes that you accommodate in the fish tank.

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