Got him today!!
And he's in a bit worse shape than I was expecting.
I am planning on doing daily almost 100% water changes for about 10 days just hopefully to stop the rot and begin healing.
I originally was planning to put him my 2.5 moss tank but I'm worried about if the salt will bother the moss.
So new plan is to keep him the half gallon he came with for the next 10 days and hopefully with daily wc and keeping him warm he'll turn around. Think he will be okay in the .5 gallon for short term?