definatly get a refractometer, you can find some online for like 40 bucks. the thing is about hydrometers, even if you test them, they do get more and more inaccurate over time because of build up and wear. If you are using a hydrometer, get a refractometer, if you cannot do taht at this moment, then ocne a month wash out the hydrometer with rice vinagar to remove build up.