If you've been topping off with SW
and not distilled, then your salinity to going to be too high. Looking back on this thread, doesn't sound like you were ever measuring salinity so it wouldn't surprise me if your hydrometer was reading close to correct.
As far as air bubbles... those should be obvious - just give the hydrometer a good slam on the table when you set it down and the air bubbles should dislodge.
You could always take a sample to a LFS
and have them give you a reading to compare yours against.