The pH value represents the acidity (alkalinity) of water. The pH value is a measure for the acid or alkaline character of an aqueous solution.
A pH measurement is one of the most important measurements in an aquarium. It is extremely important to compare the measured pH value to other measurements of previous days, always taken at the same time, since the pH value varies greatly during the course of the day (e.g. from illumination).
The pH value inside the aquarium should be kept as constant as possible. One option to do so, is to stabilize KH in the range of 7-10°dH. The alkalinity (KH) buffers the pH value and thereby avoids pronounced pH fluctuations.
A pH value between 8.2 and 8.4 is considered optimal for a salt water aquarium. The GIESEMANN pH test was specifically developed for this pH range in salt water aquariums.