Fish stop eating

Question
Hi my name is Dwayne and I'm very concerned about my tropical fish(Mollies)...thing is, all of them are very healthy and never show any signs of sickness...but every now and then one of them will just stop eating...swim aimlessly around then tank, start resting at the bottom quite often and then just die a week or so later....it's happened 6 times now , and no matter what I try, nothing works.....I'm starting to lose most of my Mollies, my other fish are fine and it's just the Mollies that's giving me trouble..
If there were any signs that they are sick, I would probably know what to do, but there are no signs, they just stop eating and then get thinner by the day and then die..

Please help as I've given up.....

Answer
Dwayne,                                                      Are you using aquarium salt they need it. It is cheap and 1 tblspn per 5 gal. It helps them relive themselves of liquid wastes. They drink water by absorbing it and and releive themselves by letting it out thru their body this is osmosis.Do this I think it will help. good luck, tina