even though I can't give you an answer, you might be able to get one alot faster if you post your water stats - ammonia, nitrites, nitrates, ph, temp, any other symptoms, tank mates, etc.
I found this in the pinned topics. See if this helps...
Septicemia: A fairly rare to common in all tropical and coldwater fish. It is caused by bad tank conditons and is very hard to cure if not impossible. Bacterial Hemorrhagic Septicemia can be diagnosed by red streaking of the fins and body and once this disease progresses, ulcerations and body sores start to appear. There is significant loss of appetite, lethargy, loss of motor functions in the later stages of the disease.
Treatment: I recomend using Oxytetracycline Hydrochloride Powder obtained from a vet to cure this disease.
Scout, did the first part of what I coppied and paste sound at all like what you are dealing with? I realized i coppied too much (part of another disease) so I will be going back and editing that out.
Earlier he had to big red spots on each side of him. Now he has very very small red spots on each side with pink with it. I did a 75% water change. The air conditioner off. My apartment is kinda cold but the temperature in the tank is the same.
It sounds like your fish doesn't have septicemia yet, so that's a good thing. What he probably has is an ordinary bacterial infection which you can treat with the medicine you showed on the link, or MelaFix might even work. If you can get Kanamycin, which is sold as KanaPlex, that would be best of all.
What you have is 3 goldfish in a small tank, and since they are big eaters, they poop a lot and pollute the water. This can well be the reason for the infection. Once it is cleared up, it would be a good idea to double up on your water changes until you can get a bigger tank for them.
I asked about the temperature because if it warms up and gets cold, then warm, then cold, it puts a serious stress on them and makes them more likely to become weak and sick. Luckily for goldfish, the cold won't bother them at all, provided it stays close to the same temperature.