"Salt shimmy" help

Is there anything else besides deficient salinity levels that will make a fish do the "salt shimmy?"
Some of the livebearers at work will do it and I'll check their salinity and it's totally fine(we try to keep it at 1.002).
Now, my chromide is doing it at home. I keep my salinity between 1.005-1.006. Both the tanks at work and at home are water changed once a week at about 25-30%. :huh:
Should I be checking anything else? None of my other fish at home are doing the shimmy and at work, only one out of 3 connected tanks is usually affected.

If anyone's curious, I happened to solve the problem on my own. I came home today and found a multitude of dead fish. My chromide, 2 celebes rainbows, a limia and one neon swordtail. Everyone else alive (except the gobies) had begun the salt shimmy, too. Tested the ammo and pH. Ammo was the slightest amount, barely colored the water. So, I tested for nitrite thinking that maybe my tank mini-cycled and it was the on the tail end since there wasn't a lot of ammo. BINGO! My tank was mini-cycling and I had no clue. My past experience with unexpected mini-cycles has been that the fish stop eating during the ammo spike of the cycle. My fish did not stop eating at all. And in fact, I was the indirect cause of the mini-cycle. One of my bio-wheels had become incrusted with calcium and salt deposits, incasing the impeller and making it imobile. I took the filter off thinking that the tank would be okay with one filter while I took care of the other one. I guess not.
Lesson learned.