Coral bleaching is a natural process that a coral goes through before turning white as if it has been bleached. When you see that one or more of your corals have turned or are beginning to turn bleach white, be warned that this is a sign of stress.
The most common foundations that cause corals to get stressed are in increased ocean temperatures, polluted water conditions, overexposure to sunlight and exposure to air.
From a stress related cause the coral bleaching process involves algal pigmentation (zooxanthellae) living in the coral tissues to expel, and when this happens the result is a loss of cells.
Once a coral begins to bleach, consequently it begins to starve itself from nutrients. If the bleached coral is not severe it is possible for it to recover, evidence of this can be linked to true events that happened in the Great Barrier Reef when mass coral bleaching occurred in 1998 and again in 2002. If the coral stress continues however, the algae will persist to expel and this will lead to the death of the coral.
To prevent a coral skeleton, try identifying the cause of the stress to your coral and try to address the problem as best as you can, doing so will help to reduce the stress the coral has encountered and with a glimmer of hope to recover.