28230 GH-Test Suesswasser/Freshwater

Total Hardness test for freshwater aquariums

Measurement 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 concentration of these salts is low, the water is referred to as soft water, if the concentration 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. You can find a table for converting this unit into other common units in the instructions for use. 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 freshwater aquarium. Ask your specialist retailer for the correct water hardness level for your fish.

Contents of package

  • 20 ml/0.68 fl.oz. of reagent GH
  • 1 glass cuvette 10 ml
  • 1 dosing syringe 5 ml
  • 1 instructions for use
Content GH-Test Süßwasser/Freshwater

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 each drop), until the colour of the solution changes from PINK to TURQUOISE.
  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:

Tabelle/Table GH-Test

How to correct unfavourable values

If the total hardness level 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 total hardness level is too low, we recommend adding Tropic Marin® PRO-DISCUS MINERAL to increase the hardness.

Other Tropic Marin test kits


In order to protect the environment, the reagent for the total hardness test is also available in affordable refill packs!