Why isn't my coraline algae growing!

[Reefie]

I had the same thing in my tank when it was about 4-5 months old.

Purple Up won't really work unless you had a bit of Coralline to begin with.

You need to "seed" the tank with a bit of Coralline to get it going. Try getting a shaving of Coralline from another tank or even your LFS, then chop it up into as small as you can get it and drop it into a high flow area of your tank. This will spread the Coralline throughout your tank, if you have sufficient Calc, Alk, Mag it will grow.