We have an inground salt one too so like nickle it cuts down on the chemical side. However we do still use chlorine in it (from memory and dont quote me here as this is DH's department) about 10ltrs a week. This is in the height of summer when we have about 10 boys a day nearly living in the thing!
Our creepy crawlie and pump run for four hours a day, in winter and in summer about 7-8 hours depending on how much swimming there has been, so it stays relatively clear and pretty much looks after itself.
I would recommend you put your timer on to run after 10 at night. We used to have ours going in the morning and when it was first switched over to night time I noticed $100 difference per quarter.

Take a water sample into your local pool shop and they will be a wealth of knowledge on what you need to get it back into shape.