Leather in Trouble

Have a problem, that I can hopefully get some help/advice on. I have a Leather (I think it's a Nepthea), that has developed a couple wounds on the sides. This is a new coral. Params are good (PH 8.4; SG 1.025; Ammo/Nitrites 0; Nitrates 5). Nothing has stung it - no corals near.

It's been openning, but not as much today. Does it have a disease? If so, how to cure? Some type of nudibranch eating it (have found none)? Just normal shedding from stress?

Before I got it, it may've been exposed to air for a bit - original tank cracked and drained.

I know leathers can be toxic (I have only softies, no SPS), should I run Purigen or Chemi-Pure to keep water clean?

First picture shows the white wound on the stalk. Front photo shows just white area, that's developing similar wounds.

Thanks.

Thanks for the info. The wound does not seem to be expanding. I can see no signs of nudibranchs or anything else eating it. Also, no black areas - when lights come on, it still expands and opens polyps.

For now, I'm just going to leave it be and watch it closely. I will also invest in a bag of Purigen, just in case leather releases any toxins (all other corals look fine).

You can't see in picture, but I have Koralia Nano mounted to right top side of tank, indirectly blowing over leather. My long polyp leather loved it - too much - to where it out grew the tank (shading a good 1/4-1/3 of tank), and sadly had to be traded to LFS.