My pool has been treated for everything but no matter how much chlorine I put in, the test says its low?

I have treated my pool for everything from phosphates to algae and now when I test it, the chemicals all check out good but it says I have low free chlorine. I cant get the water to clear up (still a little green) and I have shocked it plenty. I dont know what to do. The chlorine wont stablize and the water wont clear up. PLEASE HELP!