When your chlorine level is above 10 ppm, the pH test can give false high results, so don't try to fix pH levels while shocking is in process. Sounds like you're either not shocking high enough for long enough to really get rid of the algae, or you're not maintaining high enough baseline levels of chlorine. As Watermom said, if you'll post your current numbers and what ingredient it is that you're using to shock, we can help you out.

Janet