This is a common problem with saltwater chlorine generators. If your total alkalinity isn't too high, there's not a lot you can do other than to periodically add muriatic acid to bring the pH down. I have to add a gallon every week or two.
Anything that stirs the water will raise your pH as well, so if you have any water features like fountains or waterfalls, turning them off will help. And keep your returns aimed down enough that they don't stir the water surface.