Thanks for your reply regarding my algae problem . The pool is mainly maintained by a friend who lives near our holiday home . I open and close the pool in late spring /autumn . The pool is mainly used by families who rent out house in July + Aug . The pool was bought from Euro Piscine and is approx 8x4.5metres in size , 2metres depth at deep end . It is approx 3 years old built with concrete base and sides.. It has a salt chlorination filtration system [ Eurosel ] The fitration is set for 10 hours/day in the summer months. I have sometimes added up to 50kg of stabilised pool salt when the pool is opened in May/ June . i use test strips to test alkalinity , chlorine? etc when i open the pool and i add ph + or - if needed . if there is algae growth in July/ Aug our friend adds choc powders to cure the problem . Visitors are not happy if they cannot use the pool due to chemical treatment etc Sorry can`t help with current chemical levels as we are not at the house again until 31 May . I hope this extra info helps .