I’ve added a little bit of information to the site about pH and its role in aquaria.
pH – Potential of Hydrogen
pH is a measure of H+ ions in solution. It is defined as the negative decimal logarithm of H+ ions in solution.
pH = -log10[H+]
A pH value of below 7 is acidic, and indicates a high concentration of H+ ions; whereas a pH value of above 7 is alkaline, and indicates a low concentration of H+ ions.
Different species of shrimp can adapt to different ranges of pH, corresponding with the pH of their natural environment. It is therefore important to provide a suitable pH for the species in order to have healthy shrimp. However, I personally believe it is more important to provide a stable pH, as fluctuations in pH cause great stress to the shrimp.