For a reef tank, 1.024-1.026 is considered acceptable (actually necessary for some animals, like seastars). It is somewhat temperature dependant as well, as specific gravity varies with temperature. What are you using to measure specific gravity? Keep in mind that swing arm hydrometers, for example, can be inaccurate....and be sure to soak them in white vinegar every so often to remove buildup. I thought I had specific gravity in that range once, until I cleaned it....
then it was off scale. A refractometer is a good investment should you get in to reef keeping. Inverts are less tolerant of salinity fluctuations than many fish.
Personally, I would not go as low as 1.021-1.022 with inverts. It is fairly common for fish however. Regardless, I don't see the need for drastic action right now. And definitely bring the salinity down slowly over time.