Sand and Cories? Possible major injury...

Last week I switched my 12 gallon tank from gravel to sand (CaribSea Black Tahitian Moon sand). I was hoping to make a better home for my two cories, yellow shrimp and snails.

I have noticed the cories weren't as active as usual, but barbells seemed just fine. Today I saw that one cory has almost completely lost her belly Just pulled her to find it's almost a hole - all tissue seems to have been rubbed away.

Ugh, this just kills me. The cories are may favorite fish. Both have been removed to a temporary holding area with a smooth bottom. All other tanks are gravel and not great for QT (of course, as it happens, new shrimp are in the true QT tank)

To those in the know: any chance that this injury will heal? I'll be honest, it looks pretty bad.

Also - the sand feels rather smooth between my fingers (no sharp edges). I thought it would be best for the cories. Clearly, that's not the case Are there any other shrimp safe bottom dwellers who can handle sand?

I just hate that this is happening. Many thanks for any advice.

Cheers - Kalli

* I have only added Stress-coat to the water that the cories are in now

Hmmm...sounds like sand may not be the problem. I will check what I can now - I have all new testing supplies on the way from df&s right now.

The cory's belly is just a mess. The other seems unscathed. It's a pretty well planted tank with lots of places to rest (charcoal bamboo, marimo covered driftwood, etc), but they do tend to hang out in the sand most of the time.

I'll check the params I can and post in a few.

Thanks for all the input.

Cheers - Kalli

Ok, using my well-water quick strips, this is what I have:

Ammonia: not quite 0, but not up to 2.5
nitrite: 0
Nitrate: 4
Copper: 0
Total alkalinity: 40
Ion level: 0
Water hardness: 180

Could be more info than you need in some areas, less in others. All I have on hand are the strips.

Again, thanks for any thoughts.
Cheers - Kalli