My goldfish is in a U shape on the gravel..

Question
I have a very small goldfish (about 2-3 inches),Its about 2 years old now and used to share the tank with another goldfish (12 litre tank.)  that died about a year ago. I recently bought two new goldfish that are only different in colour,Same size. I added these fish to the tank 5 days ago and over the past couple of days my original goldfish has been severely ill.

His symptoms are :
Split,broken fins and tails,
His scales look broken,
Gills look quite red,
laying on the gravel on his side most of the time,
Wobbles from side to side when swimming,
He also looks quite skinny.

I think this has only happened since i added the new fish, I asked the store where i got the new fish from about it and they said it could be an internal bacteria infection.Could this be right?
They said to add some medicine to the tank to treat bacterial infections,which we did this morning.

But my fish still hasn't perked up..And he looks in a very bad way, He cant even swim straight and doesn't appear to be eating much. He just lays on the bottom curled up. (I hope he survives long enough for the reply.)

I usually have a filter for the tank and we cleaned it completely (gravel and all) only about 6 days ago. The newer fish show no signs of illness as of yet.

Could this really be a bacterial infection? If not what else could it be?

Answer
Hi Adele:  I am sorry to hear your little guy is feeling bad.  I think you have a combination of a couple of things going on.  The first possibility would be one of the newer fish is bullying the your original fish... and that would cause stress and he would get sick.  Bullying often happens at night when you are not watching so... keep your eye out for it.   I would add some aquarium salt to the tank too that will help him fight off some of the infection as well as supply him with minerals he may need too.  Make sure he is getting enough to eat.  Poor nutrition is one of the key reasons fish get sick.  With goldfish if you mix handicaps...such as bubble eye or telescope eyes with normal fish you can watch one starve to death with the other eats like a pig.  If you can I would take him out of his tank and put him in a separate container like a super large jar or even a mixing bowl... use suran wrap to cover with HOLES in it.  What did they tell you to treat him with???  He either has a bacterial infection or a fungal infection caused by stress... Also try to feed him some frozen green peas... thawed of course... if he will eat them.   keep me posted... dave