See if you can get a floating hydrometer at your local store. They're a bit better for measuring salinity than the swing arm. In the meantime, see if you can get the refract. Fish will be fine in hypo for a bit longer then expected.
What you want to look for is a refract that is ATC (automatic temperature compensation). Designed to test salt water. And measures both salinity (ppt- parts per thousand) and specific gravity. Shop around for a good price, but at aquarium stores they run about $50 with sometimes a deal at around $40. This is a good instrument to have for a hobbyist in order to improve the water quality that your fish is exposed to. Especially if you plan to go reef in the future.