Well thats an easy search on the site, but ill give you a little bit of info....i actually have pH papers that i use for water, not super accurate but they do the job for me for right now. As for changing, theres different ways, lemon juice, and other natural ways, but i heard the best is to just goto the store in the plants section and get pH up/down solution, but DO NOT use the pH up/down that you use in hot tub and such, concentration is probably high since its for HUGE amts of water