Has the pool been checked for "Phosphates"? Phosphates can enter the pool via rainfall, water tanks, animal droppings and fertiliser residue. They create an extra demand on all types of pool systems and encourage algae growth and poor sanitising ability which can make the pool cloudy and cause algae growth. Pool shops & major hardware stores sell phosphate removers. We recommend that twice a year you have the pool water tested for phosphates or simply treat the pool with a phosphate remover as a preventative measure making sure to follow the product instruction and to clean the filter once the phosphates have been collected in the filter.