Neon Damsel not doing well

Question
We are establishing a new aquarium.  6 Gals, 5 lbs. of live rock, purchased water from reputable shop.  Tank maintained at 78 degrees.  4 days after neon damsel added (first fish added) it appears to be "breathing heavily", staying at the bottom.  Spent last few days mainly at the top, presumably taking air.  Has eaten very little.  As this fish appears to be dying, do you have any suggestions as to what we should do differently?

Thank you.

Answer
James,
Perhaps you should consider getting a larger aquarium.  It's extremely difficult to maintain a consistent anything in a marine aquarium that small.  Expecially when the tank is new and going through it's initial cycle.

Best of luck with your aquarium.

Regards,
Scott Johnson
Aquarium Crazy Fish
www.aquariumcrazyfish.com