Anyway to tell how much water gain from increasing sodium?

A few weeks ago my doc wanted me to increase sodium to help with the low blood pressure.  I did, and it worked great.  I have an Aria scale that automatically syncs to myfitnesspal.com so I have a good record of the weight fluctuations since that point.  Within 2 days of the sodium increase I was about 5 pounds heavier, then I would lose 2 pounds the next day, back up a pound, etc.  The fluctuations for the most part have to be due to the sodium thing, but I have also had my calories creep up dangerously high to the weight gain area instead of maintenance.  Does anyone know of a simple way to tell how much is from sodium and water retention?  (Aside from the sore breasts and ginormous fingers?)

I don't know any tricks for telling how much is sodium weight. But I can say I have gained 8 lbs of water weight in 2 days and lost it the 2 days after once I got my diet back on track. Good luck!