My first parasite/infection (Pulsating Xenia and Lobo)

[TomHertz]

Hi all,
I'm about 3-4 months in still going through the ugly period and I'm getting a bit of a GHA outbreak. I tried a 2 day blackout to try and starve it of light (I've since found out this wasn't the way to go). I've since got 3 snails to help mow the grass and they seem to be quite effective.
For a couple of weeks since then, my pulsating xenia has been real sad. As this coincided with the blackout I assumed it wasn't happy with the lack of light. I was told any change in light can stress the corals, and they could take time to recover.
Long story short I think I have a parasite/disease, but I'm finding it very difficult to ID.
I noticed a black "legion" on the stalk of the xenia that wasn't there previously. I did a coral dip and it fell right out, leaving a wound. Whatever it is appears to be inside the coral and busting out.
The next morning I noticed a small legion on the other side of the coral and did another dip - again it fell out, this time leaving a far more substantial gash that makes be wonder if it will recover.
All other corals appeared fine the whole time the xenia was struggling.
Now legions are appearing on my lobo. I have tonight dipped everything in the tank (5-6 corals).
I have some bad photos I will post in case it's something common. I apologise for the quality however it's my first parasite/infection and getting clear macro shots of everything wasn't on my mind. I assumed I would dip and it would be ok.

 

[DanyL]

That’s a Polyclad worm - a large kind of flatworm.

I don’t know if there’s a specific treatment for them, doubt if flatworm exit or the other treatments would work on this kind of a flatworm.

from what I remember m they’re usually not very invasive, in that they aren’t multiplying into huge numbers like other flatworms do, that being said - if flatworm exit does work on them, I would be cautious to use it without being ready with a big water change and siphon everything out right after the treatment, this is to prevent the toxins inside them from being released to the water column and crashing the tank.