I hope its not mites as they can be a real pain to deal with, and I agree if it were mites you should be able to see them, or at least some evidence of their existence ie silk/web, eggs or what have you, however every time I have seen that type of "damage" it was a direct result of mites, and also I have never seen pH issues manifest themselves in such a small spotted mite like way, now I am aware my knowledge is limited, and every strain handles stress differently so please do inform us when you get it resolved, best of luck