What do i do if Ph is low alkalinity is low chlorine level is fine in pool?

add some form of alkalinity booster for sure. bring it too about 110ppm, chlorine has a naturally high pH, but the higher alkalinity addition will stop acidic compounds from attacking the pH any further. depending on how low the pH is though you may have to add a pH booster, take your water into a pool shop for an in depth water analysis.