Also, ensure it's not byopsis. Check out this link if you’re not sure or need more info on bryopsis:
http://www.suite101.com/content/bryopsis-a-common-pest-in-aquaria-a51078
If it's bropsis, you’re in for a serious battle. The only thing that's worked for my besides breaking the tank down and cleaning (starting over), is raising magnesium.
If it's not bropsis, your good. It will take some time but a cleanup crew and water changes will work. Also, answering the questions Loraine asked can help with identifying and eliminating the source.