Gravity

well
1. you dont ever want to just pour salt into your tank....it dissolves poorly like that and you can burn and/or kill your livestock very fast. You dont even want to pour it directly into the sump even.
2. if your LFS water is at 1.019 then you will not get it up to 1.024!
3. Hydrometers are not very reliable IMO. I think all hydrometers should be thrown in the trash. Get a refractometer!

I nuked my first tank doing exactly the opposite of you...my hydrometer said I was too high so I did a big water change to bring it down....well the hydrometer was wrong so I dropped it to fast too low! Killed my inverts, and a few fish on the way.

My suggestion is to stop messing with it tonight. Tomorrow take a water sample to LFS and get an accurate reading. Buy a refractometer and buy RO/DI water and mix your water changes yourself.

If your water is as low as you say it is, the best way is to do it gradual. On the next few top offs use saltwater vs fresh water. But again, make sure you have accurate readings first