I have had my tank for about 2 months and have two goldfish that continue to eat the thirds fins and tail.. the poor thing only has nubs left, is there anything i can do for it?  can i seperate it into a bowl, or something temporarily, until it has time to heal, or is it too late for that?  Please help...  :(
1. How big is your tank:  Gal / litres 10 gallon

2. For how long has the tank been set up:  2 months

3. How many fish: 3

4. What kinf of fish:  common goldfish

5. What are the water parameters:    Ammonia.........ppm
DONT KNOW ANY PARAMETERS         Nitrite..............ppm
                                                            Nitrate.............ppm
                                                            pH..........................
                                                            Temp...............degrees Celsius / Fahrenheit  79'

6. How often do you perform water changes: BI WEEKLY

7. How big are your waterchanges:      ...............80.-90.....%

8. What kind of waterconditioner are you using:  TETRA AQUASAFE PLUS

9. Do you add beneficial bacteria:  added some fresh water salt today

10. Symptoms your fish is showing:  fins and tail are gone, other fish are eating them

11. Since when does your fish show these symptoms:    it has been ongoing, he was almost healed up and i noticed yesterday they were at it again, and they are pretty well gone now

12. How is the normal behaviour of your fish:  usually it is very social but seems to be the third wheel so to speak, he is the only original fish that we bought in june, he was fine until the newer ones started on him

13. How do the other fish behave:  the other fish are aggressive, and seem to be territorial

14. Post pics of the sick fish:dont have any... will try to get some

15. Do you have a filter on your tank, what kind, how big (gallons per hour)
yes, aqua tech 5-15, dont know gph
16. Do you provide extra aeration with an air pump and air stone/diffuser of some kind. NO, SHOULD I?

 they are pretty small, only about an inch and a quarter long, the fish store said they would be fine, I have plants and things in there, but i am afraid the damage may have been done can i just put the injured one in a bowl for the time being, or do i have to have another filtering system?

Sorry to hear of your loss. To answer your last question, aeration of some kind should be provided via an airstone. It will enable your fish to live long, healthy lives.

Sometimes goldfish will gang up on a goldfish that is weaker/sicker/smaller or simply just can't fight back. Overcrowding can also cause goldfish to get edgy. Aggression, once begun, is a hard thing to stop, as I'm sure you know well. It is important to separate fish immediately when bullying is first spotted, and give ample room to the fish to begin with. The person at the store obviously didn't know that one goldfish can easily outgrow a 10 gallon tank - they get quite huge and produce massive ammounts of ammonia through their gills and their waste. How often are you changing the water? Weekly 50% water changes are crutial in an overcrowded tank until you can provide your remaining fish with larger housing. I would also advise buying a test kit to make sure your water parameters don't get out of hand...ammonia should be 0, nitrite 0, nitrate under 40ppm, and ph below 8 ppm. This will ensure your fish live in as stress-free an environment as possible until you get them a 20-30 gallon tank.

Good luck and happy fishkeeping! 

Definately bigger tank 10 is okay while they're juvenilies, but after a year you need a 20 at least. Ditto nossie.

get like 80 gallons so the fishs get fit