Blackish mark on zoa

[bevo5]

Hi there. I just noticed this little discolored area on a zoa. Overall the colony is doing very well - always wide open and it's constantly spreading out with new polyps. Is this just normal discoloration or should I be concerned?

 

Thanks.

 

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[BulkRate]

Have any hermits or true crabs stocked? Every once in a while one of mine will take a nibble out of a zoa's/paly's skirt and it looks like that for a few days afterwards.

 

Dip it in a lugol's iodine solution if it starts to spread, but otherwise just keep an eye on it.

[bevo5]

I do have a few small hermit crabs in there. Maybe one of them got a bite. I just noticed this yesterday so I'll keep an eye on it.

 

Thanks.