digi help

[charlesr1958]

Polyp expansion or contraction has many possible causes, and I doubt anyone could tell you the reason why yours is doing what is shown.

A quote from This Article

"The expansion and contraction of different species of corals is often a behavior used to moderate the light environment to maximize photosynthetic performance of the zooxanthellae. Factors controlling tentacle expansion include flow speed, irradiance level, light spectrum, the presence of prey, zooxanthellae density, polyp size, and diurnal behavior. For aquarists, this means that the degree of polyp or tentacle expansion may not be a good indicator of coral health or "happiness," but rather may be a species- or environment-specific attribute"

Chuck