In a pool your size (approximately 9,000 gallons) adding about a cup of muriatic acid should lower your ph by about 0.2. It is better to add small increments of things instead of trying to do it all in one large dose to make sure you don't overshoot your target. So, I would only add one cup of acid at a time and as my pal, Carl, said above -- take precautions with the stuff.

For alk, a range of 80-125 is a good target. You can raise alk by using baking soda as explained above. If your alk is too high, check the sticky at the top of the alk forum for the method recommended to lower it.