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Yeah check your salinity with a reliable device - they are often faulty. Your starfish shouldnt be loosing legs at 1.026 salinity, that is normal seawater strength. (unless its an estuary starfish or something?)
I agree with Nancy, it sounds like you are getting a reading that is lower than it acutally is. So try to get your Lfs to test the water or use a refractometer, so you can be sure.