Shepp41, mollies do not really need salt. What they do need, along with many other typical livebearers, is water with plenty of minerals in it. My tap water gives me readings of over 12 german degrees of hardness and all common livebearers do just fine in it. If you have relatively soft water and are trying to use it for mollies, platies and guppies, some added hardness may be in order. One way to achieve hard water is to add some calcium carbonate as either crushed shell or crushed coral to the filter flows. If you have hard water, there is no need for it but soft water sometimes requires a bit of adjustment for common livebearers.