The key to SPS is having everything stable. Flow, light, CA, ALK. Mag. Don't let things swing to much. Shoot for a tight range and keep it there. For example if you want to keep your CA at 450 then shoot for it but understand that 440 - 470 is ok. You will drive your self nuts trying to stay right at 450. I believe Flow is the most overlooked part to keeping SPS happy. They love lots of Random flow. We would need to know more about your tank to help you out more. If your doing water changes and only have a few corals I would say that dosing 2 part is not what you are missing. Need to know more about the tank.