I can't vouch for any of the 'grow coralline' products out there since I've never used them. But what worked for me is having something in the tank with coralline algae on it already like a frag plug or the shell of a snail and a high magnesium level. Just up your magnesium level and you'll start seeing coralline growing in your tank, not overnight, but it will. Make sure your other parameters are in check and that you have sufficient light and flow also.
