Hello animallover
Your turtle is exibiting classic signs of a respiratory infection. These need to be treated by an exotic animal vet. If you don't already have a vet here is a link that gives you exotic vets by state:
http://www.aemv.org/vetlist.cfm
Some things you can do until you can get to the vet are increase water temp slightly, make sure the tank is clean, reduce stress by keeping any vibrations to a minimum, make sure that he has full spectrum light.
Respiratory infections in turtles are quite serious and without antibiotic treatments they often don't recover. On rare occasion if the illness is minor taking the steps above can help. Once they start displaying the neck stretching and they stop eating they are having severe difficulties.
I am so sorry about your turtles. I do hope that he will recover.
Sincerely,
Bunny
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