I have an in ground plaster 9 X 17 kidney shaped Pool approximately 4,000 gallons. It has the AquaPure chlorine cell. Salt content about 3.1, alk 70, ph 8.4, chlorine a bit high at 8 ppm, Cya 110. Water has never been changed and was started up in 2005. Water is clear. How do I get the ph in range and also Balance the alk. Adding acid would solve the phone issue but lower the alk even more.