Get some clear tape....
Scotch tape would be good.
Pick a spot close tot he bottom of the glass and tape a few layers (maybe 2 or 3) above where you see the salt buildup. Then clean off the salt from the band below the tape.
If somehow there are drops of water running down the outside of the glass. The tape will catch it and the salt will form on the tapeline not the band....
If however, the salt apperes on the band below the tapeline.........
Borrow a tank big enough, or go to your LFS and explaine the problem. Ask if they can house your livestock for a few days while you drain, and fix the problem.
Id get a big trashcan or two from somewhere (new, clean) and drain the tankwater into it. Put the live rock in there and any other things that need to be in the water.
Then you can drain, clean and ceal the tank (id redo all of it). Its a big job, but shouldnt take more than a day.
Let the seal cure for 24 or more hours and then put your sand, water, rocks and such back in. Look for leaks.. chekc the water and then hope the LFS hasent sold your livestock... LOL