Very wise words from the man 2 posts up.
You my friend have stumbled upon one of the reef tanks greatest mysteries! Where does this stuff come from and how do I get rid of it? Safely that is! Once someone comes up with a solution, they will be rich!
There are some chemicals out there on the market that claim to have sucess with slime algea. Some actually work BUT, with every action there is an equal but oppoisite reaction. Opposite reaction, you say? Yes. I have played with these chemicals in my old reef tank. It did remove the slime but in its wake left some, not all, but some corals in very poor health. Not to mention the fact that I had to constantly run carbon after that to "polish" the water. According to the makers of said chemicals, the corals must have already been in bad health for "their" product to harm them in any way! Bull hockey!
What the man wrote above is the best advice. Current, more skimming, change old bulbs, water changes and good ol' fashion manuall removeal are the best at keeping this stuff under control.
Good Luck