pH value

In simple terms, the pH value describes whether an aqueous solution reacts acidically, neutrally or alkaline. Acids have a pH value below and alkalis above the neutral value of 7. Life generally takes place at pH values of around 5 to 10. Some extremophilic bacteria can tolerate values above 10 and others can tolerate values below 0.

It is important to know that pH has a logarithmic scale, i.e. a change by a value of 1 is a change in the pH-causing substance concentration by a factor of 10. For everyday aquaristic use, the pH should be as uniform as possible and should be in the correct range. Daily pH value fluctuations (delta pH value) of up to 0.3 are normal. Countermeasures should be considered for higher fluctuations. Possibilities for this can be found in the "Checklist KH-pH".

Possibilities for determining the pH value:
Drop tests/test sticks: simple, inexpensive, but quite inaccurate, no continuous measurement possible.
Reflectometer: simple, accurate, no continuous measurement possible
Photometer: accurate, no continuous measurement possible
Measuring chains ("electrodes"): high accuracy, continuous measurement possible, but regular calibration with fresh buffer solutions is necessary
Ion-selective chips: still too expensive

Optimal pH values:
Sea water: 8.0...8.4
Freshwater - African cichlids: 7.5...9.0
Freshwater - Amazon type: 6,0...7,0
Freshwater - blackwater biotopes: far below 5

Optimal delta pH (daily pH fluctuations): less than 0.3