I find in newer tanks < 1yr old, corraline comes and dies off quick all of sudden. As the tank matures, and stabilizes it tends to stick around longer and longer. So, I realize I left one ingredient off my list - time...... Also, as far as "you must have some corraline" goes, that's true, but if you buy a single coral, there is probably more than enough corraline on the base rock it's attached to to get it started. I find especially in younger tanks, corraline tends to grow better in the darker shaded areas, and in general tends to like lower light, however, some corraline will certainly adapt to more intense lighting.