bioned

A couple of things can be happening:

Your refractometer is being calibrated with RO or distilled water instead of 35ppt calibration solution.
The water you are mixing up is in factor more saline than your tank.
Salt creep is being scraped off various areas and pushed back into the system where it increases salinity. Any salt creep should be scraped away and disposed of.

Keep in mind that your skimmer's daily output is another area that can affect salinity, usually making it go down as replacement water is RO or RO/DI.

Thanks Marc,

Hmmm, good points. I should probably question my calibration fluid, since it's probably a bit old, but that still wouldn't affect the upwards trend it would just affect the true readings. I've eliminated most of the salt creep from the tank and do dispose of the majority of it. I've recently moved and am getting RODI water from a LFS until I get my rodi filter installed and I'm now very, very conscious of the specific gravity of the water I mix before it's added to the tank.

I think I'll focus on the skimmer output and see if there is something going on there.

I wouldn't worry about it so long as you are measuring salinity and adjusting frequently. Unless of course you are seeing crazy fluctuations on a daily basis, in that case I would stop drinking.