Just a note, sometimes keeping the pool at shock levels for a couple of days is not enough. You must check at night and see if you are losing any chlorine overnight, because sometimes even with a cc of 0, if the pool is using chlorine overnight, then it is fighting something that will take hold if you don't get rid of it completely. I have had to keep my pool at shock for 6 days so far after opeining. My water is clear, no combined chlorine, but still losing some chlorine overnight. Each night it loses less - so I think it is almost ready!!