fantail goldfish agression

Question
I have two fantails, one larger than the other.  The smaller one has been sickly, swim bladder, and I've notice quite a loss of scales on both sides of his body.  On occasion I've noticed the larger fantail sucking or nudging at the smaller one. I of course give them more attention when I'm feeding them so I don't know if this is happening at other times.  They sleep with their noses under the ornamental rock but I find the one with swim bladder, is under the rock more often than not.  I've done a 1/4 - 1/3 water change, added stress salt, water conditioners and ph balance with each water change and only tap water conditioner when I do partial water changes.  Can you tell me why the smaller fish could be losing his scales?  Could it be from the aggresive behavior that I noticed at feeding time or is this behavior not aggresion but the other fish trying to get the other sickly fish to eat or move? Could this be a disease?  I've done one treatment of tetracycline last month just in case.  Where do I go from here?

Answer
Swim bladder disease can lead to long term complications.  Fish tend to pick on sick fish to get them out of their territory, to stop the spread of the illness.  This is why a quarantine tank helps.  Sometimes, sick fish are killed by the healthy fish before they have a chance to get better.  I am not sure what to suggest other then separating them and seeing if the smaller one improves.