I went to visit my daughter and when I came back pool was GREEN. DARK GREEN. Dear hubby forgot to put chlorine in and now I do not know what to do. Been battling all summer to get a cya reading. It says 0 no matter what I do. So today I tested the ph and it was high so added acid. Waiting a couple hrs for that. My chorine says OK. More toward the ok on the low side, but thats because hubby put a gallon of chlorine in it two days ago but only a lighter green today so he says. What do I do? How much chlorine can I put in it? 4500 gal. Vinyl, he has been running the pump 24/7. I have vacuumed it to no avail. Will go out and test in another thirty min or so. I was reading that sometimes you need a 25 level to keep chlorine level up in pool to keep out algea. But is that safe to swim in? When can I go back in the water? I sure wont while it is green. YUCK