[ReefOcean]

If it is white, it is no longer algae. The white is simply the carbonate foundation built by the algae.

Many things could be causing this - not enough blue/too much white light, exposure to air, drop in KH, reduction in Calcium, change in water flow, shading, or nuisance algae growing over it.

To grow back/more, Increase the amount of actinic lighting, and the duration of the actinic lighting. Tune down white spectrum if possible (SPS permitting), Make sure calcium is around 400-420, make sure magnesium is around 1300. Turn away power-heads from locations where you want coraline to groww, it does not like high flow.


One thing to also consider is when scraping algae, mind the coraline. Just because you scrape gently enough just to remove the green stuff, it doesn't mean you are not killing off the coraline as your scraper passes over it.

Good luck.