Save you r money for something worth while.
Ensure yur tanks temp, lighting and cal and alk, SG and ph are where they should be and coraline will grow just fine without adding purple up. I tend to run all my tanks on the max end of ALK and CAL, my temps at 82-84, and ph 8.2-8.4 with 10K or 50/50 lights, SG of 1.026 and getting coraline has never been aproblem. If I bump my alk and cal and SG up during cycling period I can normally get coraline within a month of setting up a new tank....