Total Hardness (GH)

When discussing water hardness, terms like GH (Gesamt Härte, Joint Hardness) and KH (Karbonat Härte, Carbonate Hardness) come into play. Both are German terms and are expressed in the Netherlands as "degrees of German hardness." While many other countries use different units, the Netherlands uses German terminology.

We discussed Carbonate Hardness (KH) in a previous article. KH is extremely important for keeping our pond and fish healthy. In this article, we'll delve deeper into General Hardness (GH).

What does the GH propose?

The GH indicates the concentration of alkaline earth ions in the pond. These consist of more than 99% calcium and magnesium. When we refer to GH, we are actually referring to the dissolved amounts of calcium and magnesium in the pond water. This concentration is expressed in degrees German Hardness. A GH of 8 is therefore actually a General Hardness of eight degrees German Hardness (GH = 8 ºDH). The term General Hardness is confusing; it gives the impression that it also includes Carbonate Hardness (KH). However, this is not the case. GH and KH are separate entities that can be adjusted independently.

What is the importance of the GH?

Calcium and magnesium are metals that are only marginally important for the health of the pond and its inhabitants. Fish, like humans, require small amounts of these minerals. Calcium plays a role in bone formation and maintenance of teeth (in carp, this means bones and teeth), as well as the transport of other minerals throughout the body. Magnesium is important for muscles and the nervous system.

Measuring GH in the pond?

Since only a very small amount of calcium and magnesium is needed for healthy fish, there's virtually never a deficiency in a pond. Especially if water changes are carried out regularly, there's sufficient supply from tap water and fish food. Plants, however, are major consumers of calcium and magnesium. If you have a natural pond with many plants, a sufficiently high GH is somewhat more important. However, even in these types of ponds, a deficiency is almost never seen, provided water changes are carried out regularly. Measuring the GH is therefore usually unnecessary, unless you have a large number of plants and only change water infrequently. In the latter case, measuring is important, and you can use supplements to maintain the GH level. A GH of four degrees DH is sufficient for plants and animals; you'll almost never fall below this. However, a GH that is too high can cause calcium deposits, which are detrimental to pumps and heating elements.

GH and KH

Measuring the KH is therefore much more important than measuring the GH. A KH that is too low can cause a pH crash and has disastrous consequences for the pond and the fish.

Author: Joop van Tol (www.koitoday.nl)