In the current version all you need to put in is the pool volume in gallons and press calculate. The other spaces are outputs. So for your case, you should not add more than 7.6 oz of 31% muriatic acid at one time. This should lower your PH by 0.2. If you need to drop by 0.4, then you should dose twice but not together (e.g. morning then evening after measuring).
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