pH , always pH
I'll mention the topic of pH one more time, partly because I'm a scientist and partly because I guess I'm a bit anal about it. pH is always pH, never PH or ph or Ph.
The reason is, pH comes from the German "potenz Hydrogen" and in German nouns are always capitalized, and besides, chemical symbols are always capitalized. So it is always pH, even at the beginning of a sentence.
Roger (always pH) Lederer