Cal-hypo will cause clouding if your CH level is already high. On the other hand, something is consuming your chlorine, and it might be what is causing the cloudy water.
Regardless, if you gave the cal-hypo addition at least 30 minutes to mix in before testing and FC was then 0.4, you need to shock the pool. If you gave it less time to mix in it might be that you tested some water it hadn't mixed into yet.