What is your stabilizer level? Too much stabilizer reduces the effectiveness of the chlorine.
To answer your question though I would probably add about 6 oz of regular bleach ... should bring you to about 10 PPM or more and will not raise your stabilizer. I would then test the water in the AM and see if the chlorine dropped a lot (if you can test possible high chlorine - actually anyone can, just a little math) and add more if need be. The question is a hard one to answer since there are a lot of variables to the water itself and how much the chlorine is trying to kill.
