Carbonate hardness: lower or raise the KH value | manual

In order for the garden pond system to function optimally, the water quality must be appropriate. This is the only way for living things to survive in the pond in the long term. Various elements contribute to this, for which the carbonate hardness in connection with the pH value are of great importance. What this is exactly, how to measure, lower and increase the KH value is explained below.

Definition

The carbonate hardness is a value that describes the concentration of dissolved minerals in the pond water. These include calcium and magnesium in particular. Furthermore, the buffer capacities of pond water are determined by the KH values. The focus is on the extent to which the pond water can compensate for pH value fluctuations.

The pH value is an abbreviation for “potentia hydrogenii”, which means something like “hydrogen strength”. This provides information about whether there is an acidic, neutral or basic/alkaline environment in a body of water.

This basically refers to all bodies of water, so it is irrelevant whether it is a swimming, koi or purely plant pond.

Carbonate function

Carbonate is formed by binding free carbon dioxide, calcium and/or magnesium. In this way, a source of carbon dioxide is created, which is used when microorganisms in the water do not provide sufficient CO2 for plant growth. If the pond inhabitants have a higher demand for carbon dioxide, the pond system uses the carbonate or the associated CO2 source. As a result, the carbonate hardness decreases.

Optimal KH value

An ideal KH value is when it is between six and eight ºdH, with ten being the maximum value that still falls within the tolerance limit. “ºdH” means the degree of German hardness, which serves as a measurement for the carbonate hardness.

Basically, the higher the values ​​are within the optimal range, the more stable the pH value of the pond water is. If this is between 7.5 and 8.5, that’s ideal.

At the same time, the total hardness, GH for short, plays a decisive role, which refers to the amount of dissolved minerals in the water. If this gets into an area that is too soft, there are increasing restrictions and, in the worst case, biological processes in the garden pond are stopped.
For this reason, the KH value only provides information about the existing water quality in connection with the GH value and must therefore always be measured together.

Importance of different carbonate hardness values

Less than five ºdH

  • definitely too low value
  • can have serious consequences for all pond inhabitants
  • leads to fluctuating pH values
  • nitrite and ammonium in the water reach toxic levels
  • many algae are formed

Fünf ºdH

  • acceptable value
  • stable pH
  • Self cleaning still works
  • Regular measurements at shorter intervals are advisable so that the value does not drop below five ºdH unnoticed
  • recommended: set the KH value a little higher so that the boundary between good and bad value is widened

Between six and ten ºdH

  • optimal values, with ten also still being in the acceptable range
  • natural self-cleaning of ponds works best
  • pH is stable
  • balanced balance of CO2 and minerals ensures optimal supply for plants and underwater animals
  • From ten ºdH, regular checks should be carried out based on the limit value

Between eleven and 14 HdH

  • slowly critical KH value
  • smaller pH value fluctuations affect the water quality
  • as a rule, the water slowly becomes cloudy
  • The natural self-cleaning function decreases visibly the higher the carbonate hardness value increases

Higher than 14ºdH

  • definitely too high a value (rarely occurs)
  • milky water
  • little to no more sight of fish
  • Pond creatures suffer from the too high value
  • natural self-cleaning system no longer works
  • Lime-sensitive plants can die
  • some biological processes slow down
  • Pond filter pumps and similar technical equipment can be damaged

Lower KH value

If the carbonate hardness value is too high, it can be reduced in various ways:

  • Partial or complete water change of the pond with well water or water from the rain barrel
  • run extra soft water daily (best used in summer when a lot of water evaporates)
  • During the rainy season, drain the pond water a little every day and have it refilled with the rainwater
  • special UVC lamp to reduce the KH value only with existing filter pumps – the higher the wattage, the faster the reduction, but also higher electricity costs
  • Reverse osmosis system – it extracts up to 95 percent of the minerals from the water
  • Products for lowering the pH, with which the carbonate hardness is to be lowered at the same time (dose carefully so that the KH value does not drop too low
  • Peat – also lowers the pH value – less recommended due to the environmentally harmful extraction of peat from bogs
Tip: If pond water with a high carbonate hardness is drained into the garden, attention should be paid to the surrounding plants. Many plants do not tolerate hard water and could then die under certain circumstances.

Increase carbonate hardness value

If the KH value is below five ºdH, which usually occurs in newly created and/or stagnant ponds, then this must be increased to the optimum range of between six and ten ºdH so that fish and plants remain/become viable.

KH values ​​can be increased in the following ways:

  • Shell grit (actually supplementary feed for chickens) contains a lot of lime and naturally increases the carbonate hardness
  • Limestones have the same effect (should be placed in running water, such as a filter system or watercourse)
  • In sufficient doses, chalk lime can neutralize low KH values, activates biochemical processes and has a disinfecting effect
  • non-carbonated magnesium lime has a good effect of raising KH levels
  • Special pond products from specialist retailers to increase the KH value (e.g. KH Plus from SUI JIN)
  • use calcareous tap water for water changes
Tip: It is essential to ensure that the increase in the KH value and thus the simultaneous increase in the pH value does not exceed 1ºdH per day. Otherwise the stress on animals and plants would be too great and natural processes  could be disrupted by the sudden change in situation.

Measure carbonate hardness

The specialist market offers a whole range of test sets for measuring the KH value. A product that can also be used to determine the pH and GH values ​​in addition to the KH value is ideal. So-called rapid test kits are practical. They are simply held in the water. Colors then form on the test strips, from which the individual values ​​can be read.
Alternatively, droplet tests are available. They are usually more expensive than quick tests, but are much more accurate in the measurement.

Conclusion
The carbonate hardness is extremely important for all types of ponds – not only for the viability of plants, fish and/or other pond inhabitants, but also technical equipment such as pond pumps can suffer damage. With the methods described here, values ​​that are too low can easily be increased and values ​​that are too high can be reduced.

Kira Bellingham

I'm a homes writer and editor with more than 20 years' experience in publishing. I have worked across many titles, including Ideal Home and, of course, Homes & Gardens. My day job is as Chief Group Sub Editor across the homes and interiors titles in the group. This has given me broad experience in interiors advice on just about every subject. I'm obsessed with interiors and delighted to be part of the Homes & Gardens team.

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