I agree with Adam.
In my experience, these animals can withstand a wide range of salinity, especially if it changes relatively gradual, but if it's gone down closer to fresh water, the best way to help our salt water pets is to raise it even more quickly than it dropped, to a point.
Frankly, if it were me, I'd check the salinity to see how alarmed I should be at what had happened. I would also check it every time after each cup of salt was poured over the return pump intake screen after giving it a couple minutes to mix in the tank. I'd probably start off fast and then slow down. When salinity was around 1.015 I'd be raising it more gradual than if it was showing 1.005.
Kind of like if a sealed room ran out of O2, I'd waste no time getting some O2 back into the room, but not fill it up with O2 all at once because that could risk some kind of shock. Am I right? Anybody?
Aloha,
Mark