Fiddler Crab Shell Disease?

[Burrilliant]

I have a dying female fiddler crab who lost a number of legs during a mis-approrpiation of space with a fellow male tank-mate. She had been ok except since her trauma, shes developed large, indiscernible, light colored spots that appear to be killing her
I still have 2 surviving male fiddlers and 1 surviving female red clawed crab.
Has anyone had any experience with these spots?

Post
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So I have had by now many a Fiddler & Red crab in my 50 gallon tank within the last 2 years. Some with greater fresh air ambitions, some not as great. Zero have lasted long r than 9 months.
Some of my fiddler crabs have been subject to what seems a shell/bacteria disease (9++).
I've had several crabs now seemingly subject to the same shell/flesh/bacteria disease. Each has died within a few weeks since its first spotting.
So yes, please do understand that this specific crab suffered severe stress when it was cornered within the confines of the water-heater by a larger, more aggressive male who managed to snip its 4 right legs before I realized what was happening . That said, this is the 3rd (THIRD) though multisexed crab to die in my hospice .
Its on my desk, which in my mind is trying to air out before I put it back in the tank.

Any thoughts? Have you ever seen such spots before? I haven't seen then ANYWHERE!
Not in nature, or captivity. #136###? Why only in my tank? Why doesn't it go away after nominal captivity?

A couple of pictures, as best as I could capture.

Best resolution in an attempt to feed brine shrimp:

For less contrast, more realistic, water-free pics:

Since then, the shell condition has developed. What does it mean?
Is there anything I can do? Can they be saved? Should they be removed?
I have looked at many shell conditions, but never seen anything like these spots!!

If you can find a way to get these spots to subside and the crabs to live, I have a monetary bonus for you !!!!-Burr
Thank you for your time!
-Burr

 

[This Old Spouse]

I think that since this keeps happening, you should wait until the last one dies (or put it out of its misery) and break down your tank. There's an obvious problem here, but since you can't pin it down you should just start over. If you get into it again, sterilize the tank and use new substrate, etc. There's something in the environment that is harbored in your tank, and just replacing crabs is not the way to go.

I did some research myself and couldn't find anything to describe these spots or what could cause them. Can you describe everything about their environment, what you feed them, etc.?