Please help! Oranda goldfish has huge belly, with red spots

i forgot to mention, when we repeat the antibiotic treatment, we noticed her scales were a bit looking upward, we searched and it looks like pineconing...
we also think she has fin rot, because last 2days we saw a small hole in her tail, and her tail ends look like it was bitten or something...

i'm unable to upload a video on how she swims today, i'll try to get a clear picture...
 
its so sad, she already died 15mins after I posted my message above..
Im just watching her swimming slowly, then her body kind of twitch a little while floating and then she stopped breathing,....

do we need to make a water change for the other goldfish?.. charlie, the other goldfish, is fine, I mean he looks fine, no swim bladder disease, he doesnt float upside down no pineconing of scales...
thanks..
 
AquariaCentral.com