Coraline growth 101.
First you must have it present in the tank. Unlike other algae which seems to come out of no where coraline must be present in order to grow.
Your calcium and alkalinity must be within the excepted range for maximum growth. More stable parameters equals better growth. Lower than excepted range equals stunted growth. Higher out of range will not speed growth. The excepted range for Calcium is 380-450 ppm....ish. Alkalinity is 7 - 12 dkh .....ish. If both those are between those numbers and remain stable there you will get optimum growth.
Lighting is really not that important as far as intensity. The spectrum is relevant and anything within the range for photosynthesis will promote growth. With the optimum growth being somewhere around 5500K-10,000k. IMO actinic lights don't promote it's growth. At least not as if it's better for growth. Extending the photo period is though. This, I believe is a wives tale that has recently popped up. Does it grow under actinics? Yes...but not optimally.I believe this myth popped up with the way Coraline naturally grows...which gets us to the next important thing to understand.
Coraline grows by spreading outwards. When there is only a tiny bit available to grow growth is slow. Whenever the population increases it spreads faster and faster. This is because it can only spread at a certain rate. The larger the colonies get, the faster it can spread because it has more outward areas to grow from.. Which I believe contributes to the myth of adding actinics helps growth. People without them have had limited growth, then added them and extended the light cycle(which would be important) then seen an improved growth. When if they hadn't added them, and just extended the light period, they would have seen the growth any ways. Because the colony is larger and the growth period had been extended.
