In a 33,000 gallon pool, it is going to take about 26 oz. of muriatic acid to lower the ph by approximately 0.2. Don't try and get to your target in one dose. Small doses (maybe a pint at a time) added in front of a return jet slowly. Be careful not to splash any on you or on your liner. Also, don't breathe the fumes. Wait several hours to let it circulate, then retest and redose as needed.