However, it is the Carbonate hardness that matters. When it is mentioned in the hobby that an aquatic plant requires "Softwater" it generally means that the plant requires low KH, this would usually also result in a low pH. Bacteria consumes it in small amounts as part of the ammonia oxidation process. It's sole purpose if any, is as a buffer to prevent tank water from getting overly acidic. KH has no innate value to most plants (some plants can use carbonates as a Carbon source and will grow better in higher KH water when deprived of other carbon sources, but this it is very energy intensive for the plant to extract carbon from carbonates rather than CO2). Adding CO2 to the solution lowers its pH, but does not affect alkalinity. As KH increases, the pH will increase as well.Īddition (or removal) of CO2 to a solution does not change its alkalinity, since the net reaction produces the same number of equivalents of positively contributing species (H +) as negative contributing species ( HCO3 and/or CO3). If there are no other chemicals dissolved such water will have also have a pH of 7. Here are some examples of common compounds and whether they contribute to GH or KH. GH is around 5-7 dGH in this tank, while KH is below 1dKH. However, you can still grow them in tanks with a high GH, as long as the KH is low. Picky Eriocaulons require soft, low KH water. Aquatic plants are much more sensitive to KH values rather than GH values in the aquarium hobby. When it is mentioned in the hobby that an aquatic plant requires "Softwater" it generally means that the plant requires low KH, not low GH. To be precise, however, we should quote GH and KH values separately, as the two values measures different things. Therefore, it is accepted practice in the hobby that the term "hard water" refers to water that is high in both GH and KH. However, in most tap water systems, GH and KH values tend to be affected by whether the source water has contacted limestone (CaCO3), which raises both values simultaneously. You can have a high GH and low KH or vice versa either reading can be raised without changing the other. Whereas GH measures divalent cations such as Calcium and Magnesium (Ca and Mg cations). KH measures carbonate hardness (CO3 and HCO3 anions). dKH does not measure the calcium levels, it only takes into account the carbonate/bicarbonate component.Ĭarbonate hardness (KH) is often confused with General hardness (GH). One dKH corresponds to the number of carbonate and bicarbonate ions found in a solution of approximately 17.8 ppm (parts per million) Calcium Carbonate (CaCO3). Carbonate hardness is commonly measured in degrees (dKH). The higher the Carbonate hardness, the higher the pH will be in the absence of other chemicals in the water, and the more resistant the water is to downward fluctuations when an acid is added. Carbonate hardness is a measure of the water's buffering capacity the higher the carbonate hardness, the more carbonate (CO3)/bicarbonate (HCO3) ions are present. One common source of carbonates is limestone (CaCO3) water that has flowed through limestone areas is high in both Calcium and Carbonates. Carbonate hardness (KH) is a measure of water hardness caused by the presence of carbonate (CO3) and bicarbonate (HCO3) anions.
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