Higher CYA is recommended for SWG pools because the cells produce chlorine slowly. It helps protect the chlorine from the sun. There are other reasons which better chemists than I can explain, but you'll notice that the Minimum and Target FC are also lower for SWG pools. I've read that is because of the high chlorine content within the cell, which I've never fully understood. I'm sure the experts will be along to explain this in better detail.