Red serpent starfish is dissolving

[Mz. Fix It]

I have had my red serpent star for a little over 4 months with no issues. However, over the past 3 or 4 days I have noticed a few white spots on her. Then yesterday there was a hole on her side. This morning her body is gaps of missing tissue. I have a community tank with no aggressive fish so no one has picked on her. I thought she was dead this morning and picked her up and she started flailing her arms around so I set her back down. She moved a couple of inches but has rested in that spot since then. I feel in my heart she is not going to make it but I cannot bring myself to remove her when she's still alive. The only thing that I have had a challenge with is keeping my alkalinity up. Could alkalinity dropping cause anything like this? Anyone that can offer up any suggestions about where I could have gone wrong with this most spectacular creature I would greatly appreciate the advice. She has certainly been the focal point of my tank. She has normally stayed hidden under and around rocks but has always come out to get her shrimp and squid bits. Over these past 3 to 4 days she has stayed out in the open as her body has continued to "dissolve" for a lack of terminology. The darker image is today where half of her body is gone. The clearer pictures are from yesterday when she appeared to only have one spot/hole in her body.

 

[AcroNem]

If there is no aggression, where something is attacking it, then it could be several things that caused it. Sea stars can be very sensitive to changes in water chemistry and can stress/ kill them. There are diseases that sea stars can contract as well, both viral and bacteria that can cause them to "dissolve", and we likely won't know what caused this specifically. All you can do is try to keep everything as stable as possible, once they degrade to that point it's unlikely to recover. I'm very sorry about this, I love brittle and serpent stars.

 

[Mz. Fix It]

If there is no aggression, where something is attacking it, then it could be several things that caused it. Sea stars can be very sensitive to changes in water chemistry and can stress/ kill them. There are diseases that sea stars can contract as well, both viral and bacteria that can cause them to "dissolve", and we likely won't know what caused this specifically. All you can do is try to keep everything as stable as possible, once they degrade to that point it's unlikely to recover. I'm very sorry about this, I love brittle and serpent stars.

Hey AcroNem

If it were to be bacterial infection is there a treatment for a long shot chance to help? She just got a burst of energy and is making her way across the tank. It pains me to watch.

 

[Mz. Fix It]

This was just taken of her moving

 

[AcroNem]

I don't think it will come back from that, I'm surprised it's moving around. I also don't think it's a viral or bacterial form of sea star wasting, I just added that information so you could research on your own or have it for future sea stars you kept. As for that there is no real remedy for the viral kind, I know Baytril injections have helped with bacterial. If this isn't something that started eating it It's likely a result of stress from big swings in parameters or something else in your system. You're sure nothing has been attacking it? Those first pictures look like something took a chunk out of it.

 

[Gareth elliott]

Echinoderms are odd they use a strange water vascular system that is very slow conpared to most animals. As a result they acclimate to changes on an almost per cell basis as its vascular system catches up. Because of this tissue necrosis also begins at cellular level and advances as fluids are shared.
I have only had necrosis experience in fromias but from that any necrosis has always been terminal. Caveat always started with the legs for me not the disc, does look like something took a bite out of it.