Ive got a school of neons in with my mollies. I use the neons to keep my hospital/fry tank to keep it cycling when it is clean and non one is in it.
When not keeping the spare cycling, they are in my main tank. Like now.
They live fabulously with my mollies. There are probably other issues here you need to discover, such as illness or water probs.
BTW you do not need salt with mollies, just leave it out. Its an option not a necessity.
*edit - sorry I did just see that your petstore advised you wrongly, as they always do. But, at least you know have come here! Not all petshops are bad, but most give poor advice due to lack of real knowledge. Many people actually do think and argue that a tank cycles without fish producing ammonia, or ammonia itself. Its wrong. The nitrogen cycle cannot take place without that key element - ammonia.*
When not keeping the spare cycling, they are in my main tank. Like now.
They live fabulously with my mollies. There are probably other issues here you need to discover, such as illness or water probs.
BTW you do not need salt with mollies, just leave it out. Its an option not a necessity.
*edit - sorry I did just see that your petstore advised you wrongly, as they always do. But, at least you know have come here! Not all petshops are bad, but most give poor advice due to lack of real knowledge. Many people actually do think and argue that a tank cycles without fish producing ammonia, or ammonia itself. Its wrong. The nitrogen cycle cannot take place without that key element - ammonia.*