Try googling Coraline algae propogation. Interesting info.
I have a lot of coraline on my LR, but how it happened is totally beyond me, to be honest. I have never added a supplement or corrective chemical, so I can't vouch for the safety of any of the info. But I do believe if you can read between some lines about keeping phosphates low and calcium up, google those for natural enhancers...
When you go to purchase LR, be sure to look for fresh rock that shows some growth. It will seed.