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An optimal pH-buffer in freshwater (both in aquaria as in ponds) is ob-
tained with a KH between 6 and 8°DH, in seawater with a KH between
8 and 12°DH. When the KH is above 12°DH, also the pH will be relati-
vely high, and so you can lower both values in freshwater with Colombo
pH-. Is the KH lower than 6 or 8°DH, you can increase it with Colombo
KH+.
Total Hardness (GH)
Test procedure:
1. Take a water sample of 5 ml.
2. Add 5 drops of GH-1-test fl uid and mix; the sample should be dark
red to purple.
3. Add 1 drop of GH-2-test fl uid and mix each time. When the sample
turns blue, the GH is lower than 1°DH.
4. Add GH-2-test fl uid drop by drop and mix, until the sample turns
blue.
5. The number of drops added to induce the colour change from dark
red/purple to blue, is equal to GH-value in °DH, so 2 drops =2°DH,
3 drops = 3°DH and so on.
GH-2
20ml
15ml
10ml
5ml
x = 1˚ DH
5
GH-2
20ml
15ml
10ml
5ml
4
20ml
15ml
10ml
5ml
3
5 dr
ops
20ml
15ml
10ml
5ml
GH-1
2
5 ml.
20ml
15ml
10ml
5ml
1
