You need to measure your chlorine after the sun is off the pool in the evening and again in the morning before the sun hits the pool. If you've lost more than 1 ppm of chlorine in that time, then you still have live algae and need to raise your chlorine again to shock level. If not, then you'll just have to be a little patient, because the chlorine kills the algae, but it's up to the filter to get it out. I'm assuming you have a sand filter--have you tried the handful of DE trick to start filtering out some of the finer stuff?