Do you have livestock yet? If no and this is a new tank, raise away till you hit your mark. If you have livestock in the tank, continue as you are, slowly.
I prefer to keep my ATO salt free. When I need to raise my salinity, I just add 1/2 - 1 cup of salt to about 1/2 gallon of RODI and wait until it's totally mixed. Then I just pour it into a high flow section of my tank or sump. I give it about 24 hours to fully blend and evaporate back to correct volume before I test again.
You should make notes of how much you need to add to your tank to raise the salinity. For instance, if you add 1/2 cup of salt, your salinity is raised by x amount. Then when you want to raise it in the future, you know exactly what to add. I use an app called Aquarimate on my iPhone and have numerous notes for these type of things.