Before we can give you any advice - you will need to get us the actual numbers for FC, TC, TA, CA, etc.
For a CYA of 20- you need to shock the pool to 15ppm - testing 3X a day and raising the chlorine level accordingly.
IF the PH is low - adjust that BEFORE getting the chlorine above 10ppm, as a high chlorine level can interfere with accurate PH test results.
Once you have the test results - post those. You may also want to take a sample to a pool store to test for metals (iron and copper) if you have a staining problem - just don't buy anything they tell you to buy.
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