sudden salt creep

I have maintained a soft coral and fish tank for about three years, with no problems. Just recently, large amounts of what appears to be salt, have somehow found there way to various parts outside the tank and to the outside tank glass.

I was wondering if anyone has experienced this or might have any thoughts about it. Everything otherwise seems normal, and all the equipment seems to be operating well. Nor have there been any recent changes in the fish or coral population.

55gal, live rock, live sand, Fluval 404, AquaC Remora hang-on skimmer with Maxi-jet, 2 AquaClear powerheads, CustomSealife UV sterilizer.

The deposits are clumps, a few splotches encrusted on the outside of the tank, along the skimmer, and I guess have somehow traveled even to lower areas of the outside tank glass. It all just started about a week or two ago.

I do regular water changes, using distilled water. Same routine for years, with no problems and nothing like this. The only other salt accumulation was a fairly steady minor amount just near the skimmer inflow.