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Total Hardness Test for fresh water aquariums



Measuring range & accuracy

Measurement range: 1 - 20 °dH

Accuracy: 0.5/1 °dH


About total hardness

The total hardness (GH) constitutes the amount of dissolved magnesium and calcium salts in the water. If the volume of these salts is low, the water is referred to as soft water, if the volume is high, the water is referred to as hard water. The reading is usually given in degrees of German hardness (°dH), whereby 1 °dH equates to 10 mg per litre of dissolved calcium oxide. The concentration of these salts in the water affects the organic functions of the fish and plants. Therefore, it should be tested on a regular basis.

The optimum total hardness value depends on the species of fish. Many African (e.g. aphyosemion) and South-east Asian species (e.g. trichogaster) cope with hard water easily. On the other hand, South American tetra, for example, need soft water to feel comfortable. A hardness level of 3-10 °dH is favourable in a fresh water aquarium. Ask your specialist retailer for the correct water hardness level for your fish.


Package contents 

  • 20 ml/0.68 fl.oz. of reagent GH

  • 1 glass cuvette 10 ml

  • 1 dosing syringe 5 ml

  • 1 instruction for use



Instructions for use

  1. Shake the dropper bottle before use!

  2. Rinse out the glass cuvette with tap water and then several times with aquarium water.

  3. Fill the glass cuvette with exactly 5 ml of aquarium water using the dosing syringe.

  4. Now add the GH test reagent drop by drop (shake the cuvette after every drop), until the colour of the solution changes from RED to GREEN (refer to the colour fields on the packaging while doing this).

  5. The number of drops indicates the total hardness of the solution in °dH, e.g. 8 drops = 8 °dH. To increase the accuracy of the measurement, a 10 ml water sample (instead of 5 ml) can be used. In that case, 1 drop corresponds to 0.5 °dH, i.e. 15 drops = 7.5 °dH.

  6. Rinse out the glass cuvette and the syringe thoroughly with tap water after the measurement process.

Shelf life and storage:

6 months after opening. Store in a cool, dark place.

Schedule of water hardness:



Measures in the event of unfavorable values

If the GH value is too high, we recommend exchanging a proportion of the water for soft water. Ask your specialist pet retailer for advice regarding this. If the water hardness level is too low, we recommend adding Tropic Marin® Pro-Discus Mineral to increase the hardness.

Frequently asked questions

Answers to frequently asked questions about this product can be found in our FAQ section.

Container sizes

GH-Test                            Art. Nr. 28230                                                   Refill Pack                       Art. Nr. 28774



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