How do i raise my salinity w/o killing anything?

[roadrunner]

I have my water change water all setup ready for my water change but i noticed that the tanks salinity is around 1.018 ish. The water change water is set at 1.021 ish.
What i want to know is how i can easily raise the salinity in my tank without killing my livestock?
If i made the water change water today . . . can i use it now to slowly raise the salinity or do i have to let it settle?

 

[fishman830]

top off with saltwater, very very low salinity though

 

[roadrunner]

I acclimate my fish by doubling the water it came in, through the use of a shot glass pouring my water in the container every minute.
Can i use this the same as raising my salinity? Just spacing the time period out further?

 

[007]

If I ever need to raise salinity, I just don't top off for a couple days until its where I want it. Its a gradual increase and avoids shock to the animals.