Help! Sick Dragon Goby!

help my sick dragon fish

I have a sick dragon fish. I bought 2 dragon fish from Wall-mart several months ago and they were both doing fine in my 10 gal. brackish tank, until 2 days ago. Now the bigger one is breathing hard and is staying in a twisted position. It looks fat and its stomach is much bigger than the other dragon fish. I have been feeding them once a day a combination of blood worms, freshwater flakes and goldfish crisps. What can I do to help my sick fish? Thanks, Maralee

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What's the SG, Hardness, pH, nitrates? Sorry to say but that looks too far gone, but hopefully you can keep the other from following.
 
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