7.3
Checking the set pH value
• Press "pH" button: The green LED next to the button will flash; the display shows the set
pH value.
• After 3 sec. the actual value appears again on the display, the green LED switches to conti-
nuously lit mode and the controller resumes normal operations.
8
Control operations in normal operating mode
Example 1: Current pH value in the aquarium = 7.5. You set pH 6.8.
The green "CO
2
supply" indicator lamp lights up.
The connected CO
2
solenoid valve is open
and CO
2
is supplied (according to the number of CO
2
bubbles per minute set beforehand on the
needle valve of the pressure reducer). CO
2
is supplied until a pH value of 6.7 is attained in the
aquarium, after which the pH-Controller switches off the solenoid valve.
Example 2: Current pH value in the aquarium = 6.5. You have set pH 6.8.
The green "CO
2
supply" indicator lamp does not go on. No CO
2
is supplied. Only when the pH
value in the aquarium rises above 6.9 will the pH-Controller reactivate the supply of CO
2
.
9 pH value, CO
2
content and CO
2
supply level
9.1 Why it is possible to set the pH value with CO
2
Some of the CO
2
content in water dissolves to form carbonic acid, thereby lowering the pH value.
The extent to which the pH value is lowered is determined to a substantial degree by the
carbonate hardness. The carbonate hardness acts as a buffer and thus counteracts lowering of
the pH value. A precisely defined correlation always applies between CO
2
content, carbonate
hardness and pH (see table). When two values are known, the third can be calculated.
9.2 Setting the right level of CO
2
supply and the right pH
For magnificent plant growth, Dennerle recommends a CO
2
level in the aquarium of between
15 and 30 mg/l, whereby
20 to 25 mg/l is ideal.
• Measure the carbonate hardness of the aquarium water (tests available from specialist
retailers).
• Read the pH value which corresponds to the desired CO
2
content from the table.
Enter this pH value on the pH-Controller.
Example: Carbonate hardness 4 °d, recommended pH 6.8.
Important note: Only set such pH values and CO
2
content levels as are tolerable for fish accor-
ding to the carbonate hardness. Should you wish to set a pH of 6.5 for certain species of fish,
for example, the carbonate hardness should be lowered to 2-3 °d. The CO
2
content should not
be higher than 40 mg/l on a prolonged basis.
See also the relevant literature on this subject or ask your pet specialist!
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