First, coralline algae needs to be introduced. It will never grow if it's not present to start with. That's not necessarily for you, but for whoever is reading.
Second, coralline is not a high light algae. How long has the halide lamp been over it? From the beginning? It can easily be killed off with powerful lighting.
All you need to grow coralline is a 15 watt curly Q energy saver bulb.
third, i agree with the above about being able to grow coralline under lower calcium levels. Alkalinity is another factor. Alk
swings can kill it off too.
I would just do weekly water changes (this will help with the cyano
too) and not add anything. it will grow back in it's time.