I think it is slightly more complicated than that. You will have to make the replacement water slightly more salty than the tank if you want the salinity overall to raise to 1.025. Try making the water in the bucket 1.026 or even 1.027.
ps- if you have a doser, I'd even set that up to add the new saltwater. If you don't have one, you can easily make a crude one by using an old (clean) gallon jug. Just poke a hole in the bottom and a hole in the cap. You can insert airline tubing in the hole in the bottom to direct the drip into the tank.