hello

waterdog

Member
It's a protective coating that the corals produce, kinda like a fish's slime coat. In the real reefs there is a lot of sand and debris kicked up and this settles on the corals. This dust is both irritating to the coral's tissue and can block out the essential light that the corals need to survive. So to protect itself the coral sluffs off this coat and starts to grow a new one. In the aquarium they can also throw off this coat when stressed out. Hope this answers your question.
 
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