Im not much of a goldfish man, but from your post history nobody else seems to be helping you out, so ill help out if i can.
I cant find anywhere from your previous posts where you have given us your water parameters. Do you have them? If not i would get a test kit asap and let us know what they are (pH, ammonia, nitrite, nitrate as a minimum). It might help steer us to what is wrong. Is it possible your tank isnt cycled? Or if it is, could the new fish have caused a mini cycle?
Ive heard of goldfish losing tails and fins in the mechanics or waterflow of the filter. Might that have happened? What type of filter do you have?