Is this STN?

[hotdrop]

I picked this frag up from a local reefer for a couple bucks and I noticed it was odd that the frag had no tissue around its base. It’s been sitting in my qt tank for about 5 days and I haven’t really seen any signs of tissue recession as it looked like this when I bought it but wanted some more knowledgeable people to weigh in and give advice.

First SPS frag I’ve owned. Night time lit with flashlight

 

[Smite]

Looks to me like old die-off or that area had be shaded previously. I say that because the dead area looks like it is covered in algae 100%. Usually there will atleast be a little white ring you'll be able to see of die off where algae hasn't had time to grow over yet. The flesh near the dead area looks healed to me.

 

[Jinko]

Could be an invasive algae, there are types of algae which grow beneath the coral tissue and kill them.
I'd probably frag it.

 

[SDK]

The bottom part of the tissue looks like it's actually encrusting back downwards, which is a good sign...

 

[hotdrop]

Thanks, I’m going to leave it alone for now and see what it looks like after a month or 2

 

[SDK]

Take weekly pics once in the display tank and compare them to this one. It really helps to have a few "time lapse" photos to judge what is going on...

 

[jda]

The frag will heal and encrust faster than it will grow back over dead skeleton. I would wait a while until it is stable from the move and then frag off the dead stuff and remount it.