You can add some Borax to raise the PH to 7.2, but you need to get the chlorine to at least 25ppm and keep it there (testing 3X a day). There is a bleach calculator that some of the members have on their signature that can assist you in the amount of BLEACH (plain unscented ULTRA bleach) to add. NO more tablets (trichlor or dichlor)- your CYA is too high and it will keep the chlorine from being as effective.

Also a 50K gallon pool is HUGE. What are the dimensions? You need an accurate # of gallons otherwise you will be overdosing your pool.