What is the importance of KH for your pond?

The KH of pond water is incredibly important. Its importance is often underestimated and can lead to a pH crash. A pH crash can cause a massive die-off of your fish overnight.

KH stands for Karbonat Härte (Carbonate Hardness) and is expressed in degrees German Hardness. "I have a KH of 7" means you have a carbonate hardness of 7 degrees German Hardness (KH = 7 ºDH). KH measures the amount of carbonates and bicarbonates in the water. These (bi)carbonates are important for maintaining a sufficiently high acidity (pH) in the pond. When waste products are converted in the filter, hydrogen (H+) is released. Hydrogen is an acid and can cause the pH to drop to dangerous levels.

The KH prevents this drop in acidity. The bicarbonates neutralize the released hydrogen. However, these (bi)carbonates are lost in the process. The KH in a pond will therefore decrease as a result of the breakdown of waste products. When the KH falls below 2 degrees German Hardness, the pH will begin to fluctuate. If the KH is completely depleted, the released hydrogen will directly affect the pH. This can happen so quickly that the pH drops to a lethal level of below pH 5 within a few hours. Most pond fish will not survive this.

It is therefore crucial that you measure your KH and ensure it never falls more than 1 degree below the KH value of your tap water. You can do this by changing sufficient water. If your tap water already has a KH lower than 5, I would recommend raising the KH in the pond slightly (for example, to a KH of 6). This can be done with sodium bicarbonate or KH+. Keep in mind that if the KH of your tap water is low, you will need to add more KH during water changes to maintain the correct KH level.

If tap water is not enough to raise the KH, you can also use KH+. 1 kilo Secret KH plus raises 37,500 liters of water by 1 point.

KH tests