Lighting, and feeding. The bad news--that's really white. May be bleached. If this is the case, feeding a variety of foods will be essential to it's long term survival. Anenomes don't need lots calcium, but they do need established tanks that are stable. If your tank isn't stable (salinity, pH), then you need to manage that. But--do you know what the supplement you have is used for? Or did you just buy it because someone said you had to have it?
In the future--please research care before purchasing an animal.