Low salinity

So, based on the salinity test we did on my aquarium water (at our club meeting in Des Moines on Tuesday evening), my salinity is quite low - 1.021 to 1.022.  I attempted to calibrate my hydrometer today (using the article we discussed) - and that also indicated that the hydrometer has been reading high.  So, I want to raise the salinity from 1.021 (or 1.022) up to close to 1.026.  I'll be doing a water change this weekend, but that won't take care of it.  My thought is to gradually raise the salinity over the next week or two weeks by doing a top-off with salt water (at the desired salinity level), instead of topping off with freshwater.  Is that a reasonable approach?  Or am I missing something?