You should bring the PH up to about 7.2, really anywhere from 7.0 to 7.4. Borax is good for that, though soda ash/PH Up will work.
Once you have adjusted the PH you need to bring the FC level back up to shock level, around 18, and hold it there by frequently testing and adding chlorine as needed. It is very important to maintain the FC level, if you keep letting FC go back down to one, or anywhere near there, the algae gets a chance to start growing again and you lose ground.
Once you have adjusted the PH you need to bring the FC level back up to shock level, around 18, and hold it there by frequently testing and adding chlorine as needed. It is very important to maintain the FC level, if you keep letting FC go back down to one, or anywhere near there, the algae gets a chance to start growing again and you lose ground.