From what I remember, if you have a school of tiger barbs, they only attack their own! and leave others in the community alone. Seems counter intuitive. I had thought my supplier was just trying to sell me lots of tiger barbs so I only bought one. Later, friends were telling me that tiger barbs are like that.

And...

If I remember correctly also...

Black Mollies can be introduced, albeit very very slowly, into a salt tank. I've never tried it, but I did have a couple in my 29 freshwater show tank.