Make sure you bring your salinity down slowly if it's too low (or raise it slowly if it's too high). I recently had that issue when I finally broke down and bought a refractometer and realized my hydrometer was reading about .004 too low on the specific gravity (which is temperature dependant by the way). Anyway, I'd just lower the salinity by about 1 ppt each day by removing around a gallon of saltwater and replacing it with fresh. I figured everything had been doing OK at the high salinity level, so there was no need to move too quickly.
And by the way, I recently took home some natural seawater from the beach and checked it's salinity. . .35, which I believe is 1.026 specific gravity at 70 degrees. If it works in nature, it works for me.