We have had our pool for about 5 years. It is a gunite IG 28,000 gallon with a Hayward S200 high rate sand filter. Bought from previous owners. We have done little to nothing except add chlorine till the water looked okay. We had the local pool company open and close it every year for us. Last year we were having a lot of trouble with the water being dirty never getting clean even when chemical levels were in good range. I am wondering if we need to do some sort of upkeep on the filter. Do you need to add sand? Change a filter? We do backwash it regularly but it is not really helping long term. Ideas??? Thanks~