Are you sure it's RTN? Pocillipora are notorious for "polyp bail". Mine do that even if just from swings in salinity. I've found that if no algae grows on the calcerous skeleton, it may repopulate. I also have them growing all over my tank now as the polyps jumps ship and move to another surface.
Dave
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Experience in aquaria, 35 years. Experience in marine, 20+ years. Experience in Reef Keeping, 6 years. Always a newbie! | 
