We need more information. Have you tested for CYA (also called conditioner or stabilzer) If it is 0, it will be hard to keep Chlorine in the pool even with the SWG working. If it is too high, you'll need LOTS of Free Chlorine to take care of the algae. SWGs are great an keeping Combined Chlorine at 0, and a maintenence level of Free Chlorine in the pool, but to kill active algae in the pool, I'd use bleach or liquid chlorinator.