I just reread the post, and the cal hypo will add calcium to the water - but probably not enough for it to be the problem. Just another thought, what is your chlorine level? I am in the process of clearing my pool which was a green mess, full of string algae, and who know's what else. My water is very cloudy - to be expected, but it is using a lot of chlorine. Even though it says I have no combined chlorine anymore, my chlorine is dropping about 10ppms per night. I have been adding lots and lots of bleach. So you may also need a lot more bleach to do the job right. I have a cya of about 40 now, and the loss is overnight, so I know it is the dead algae breaking down that is using up all the chlorine.