I see alot of posts by people that swear by stuff like puple up and i do believe it works, i think everyones tank is different and its a trial and see what happens thing.
I had a hard time getting coraline to grow until i got my calcium reactor, then it just starting growing everywhere.
Really only thing you can do is try a product that seems to have good reviews and see how it works in your tank.
I tried stuff like purple up, reef complete, kents liquid ca, etc.
calcium reactor did the trick for my tank.
Good luck!
Chris