Will this work

So im gonna do a bigger water change this week, and i have a 30 gallon tank just sitting around doing nothing, and heres what i wanna do if you correct me if im wrong, but get 25 gallons and put it in the 30 gallon tank, put my powerhead in the tank and add the salt slowly, let that sit for a day or 2 and change my water with that, will that work, cause it would take to long to mix 4 different 5 gallons buckets