Low Salinity??

[PuffLuv]

Even for a 33 gallon tank, that's quite a jump in salinity. As Doug already mentioned, it would be less surprising if the salinity went lower from evaporation. I'm guessing your just topping off with too much freshwater.

As for your skimmer, if it is a new tank, your water might be too "clean" for the skimmer to pull anything out yet. Also, your skimmer might not be "dialed-in" correctly, or if it is new, just not broken in yet.

Your hydrometer is not as accurate as a refractometer, however, they are usually consistent. In the long run, you probably want to get a refractometer. The Reef Shoppe sells them for $49 or Adam NS in Saskatoon is selling a used one.