KH
From The Aquarium Wiki
[edit] °KH - Carbonate Hardness
KH - Buffering capacity, temporary or carbonate hardness in the water.
Also known as 'total alkalinity' in some countries.
The ‘K’ in KH comes from the German word 'karbonate'. KH is a measure of bicarbonate and carbonate ions that act as buffers in the water to prevent the pH dropping or changing sharply (especially at night if you have plants in the aquarium). One degree KH is equal to 17.9 mg/I (ppm) CaCO3. It's also measured in degrees. The degree symbol may be replaced with a d (ie. 2 dKH).
- In planted tanks with a low KH value, say under 2-3d (35.7-53.6ppm), then the respiration of the plants at night can cause large pH shifts which harm and eventually kill aquatic animals. This is called pH shock.
A common misconception is that KH is a part of GH and that KH cannot be higher than GH. There is no such correlation. In some areas, the water contains more sodium bicarbonate and/or potassium bicarbonate than total calcium and magnesium. In these areas, the KH is naturally higher than the GH. Furthermore, people using water softeners will most likely have a KH that is higher than the GH, as water softeners exchange sodium or potassium ions for calcium, magnesium, and other hard water minerals.
- Sodium bicarbonate (NaHCO3) (baking soda/bicarbonate of soda) is the usual KH additive of choice. It's cheap and easy to use. It will raise pH though due to the addition of the Hydrogen.
- Potassium carbonate (K2CO3) A known food additive. This adds carbonate without raising pH. The potassium is a bonus if you have a planted aquarium.
- The ions that make up KH can be removed by boiling the water. KH makes up a component of GH, so boiling will also reduce GH slightly.
[edit] KH Calculator
[edit] Notes
This water parameter is often ignored by many aquarists. But too low a KH can cause pH shock disease and death in aquatic animals.
