Renee, there are paints which will inhibit growth for quite awhile, but the only "once and for all" measure is to remove the cause. The cause is excess moisture and a surface cold enough to bring the reletive humidity of the air near it to above 70%. That it's growing on the 2nd floor ceiling, isn't supprising, moisture will be carried there by warm air's natural tendancey to rise. What is interesting is that it is forming on an inside wall. Outside walls with poor insulation are often cold enough to cause this, but inside one's rarely are. Do you know what is behind the wall, perhaps chimney or electrical/plumbing chase? Locating and reducing or eliminating the source of the moisture may be sufficient, but you may also need more (or some?) attic insulation and insulation in the cold wall. ery often the excess moisture originates in a damp basement or crawlspace, but a lot of cooking or showering and no vent fans can also do it.