Your tank is rather ovecrowded!
The cories like to be in groups of 6 or more to be happiest, cnsiderig your stocking, I would return them rather than increase them.
The mollies do not
need salt. They can tolerate it, but do not need it. Don't add salt. For some fish it can help as a general medication when the cause isn't known but some will not tolerate it, and the cories and snails won't.
The white clouds are not tropical fish. They require cooler temperatures, much like goldfish. I would return them.
Hope this helps.