Anti Social fish

Question
We've had 3 goldfish for about 2.5 yrs. We just purchased a new goldfish at Wal Mart and added him (after letting him set in the water in his bag for about 15 minutes). The first day the other fish were fine and eating fine. Now the second day we woke up to all the fish (including the new one who's a lot smaller but not eatable to the other fish)behind a rock in the corner at the bottom and they just sit there. They're normally very social fish and when we fed them they all ate, but then they go back into the corner and the new fish is out and about his own business. What do you think the problem is?

Answer
Hi D.,
Thanks for your question. From what you have told me, my guess is that the water that came in with the fish was polluted. Please do not use chemical treatments on the fish. Buy a bottle of Cycle (organic biology, friendly bacteria) and add it to the water. Keep it in the refrigerator after you open it. You can get it at your local aquarium supply store, not sure if Walmart carries it. Please follow the emergency instructions at the bottom of my instruction page:
http://steamboats.com/aquarium.html
Be careful to keep the water temperature even asyou gradually change out the water.
If you have any further problems, please write back and we will discuss further.
Nori