16
Carbonate hardness (KH)
Test procedure:
1. Take a water sample of 5 ml.
2. Add 1 drop of KH-test fl uid and mix. The sample should turn light-
blue; when it turns yellow, the KH of the water is lower than 1°DH.
3. Add KH-test fl uid drop by drop and mix each time, until the sample
turns yellow.
4. The number of drops added to induce the colour change from blue
to yellow, is equal to KH-value in °DH, so 2 drops =2°DH, 3 drops
=3°DH and so on.
The KH is the so-called carbonate hardness or temporary hardness;
in German Karbonathärte, abbreviated to KH. The KH is made up by
forms of carbonic acid like bicarbonate and carbonate. The chemical
balance between these substances leads to a stable pH and thus the
adequate presence of these substances is essential for a stable pH; a
stable pH in its turn is essential for the well-being of the fi sh. The KH
is therefore often called the buffering capacity of the water, because
it forms a buffer against pH changes. Especial in older aquaria and
ponds, the pH and KH have a tendency to decrease, especially when
there are no or little water changes. Hence, test the KH regularly and
refresh 10% of the water weekly.
KH
20ml
15ml
10ml
5ml
4
KH
20ml
15ml
10ml
5ml
3
KH
20ml
15ml
10ml
5ml
2
5 ml.
20ml
15ml
10ml
5ml
1
