red bump on side of goldfish

This kind of sounds like the beginning of a cyst or tumor.
It could be an ulcer too or a type of viral or bacterial infection
causing red sores.

You say he's acting healthy, so I would think cyst or tumor which their is no treatment for.
They don't really cause the fish to become sick.
They do grow and get bigger over time and can possibly shorten the life span.

Is it open at all? this could mean ulcer or red sore disease caused by bacteria.

Keep an eye on him for signs of illness.

You could treat the water with a round of Melafix (recommended).
It would be safe for all your fish and could help heal the bump if it is something that can indeed heal.
It's also good at treating bacterial infections just in case he has one.

If it doesn't go away, it's more than likely a cyst or tumor.

If it doesn't go away and you already treated with melafix and he begins to show signs of illness, treat with a bacterial infection medication.

let me know how he does - I'm hear if you have any other questions or concerns as well.

Kae

It is not an open wound. Almost looks like a reddish color bump under the top layer of the skin. I removed the carbon from the filter and started with Malifex today and will see how that goes. Fish is still very active and eating normal. Thanks

Your welcome!
Let me know how it goes.

I had a comet goldfish develop a cyst/tumor (one or the other)
when it was about 6 years old.
It's still alive and living well in my mothers pond, he's 14 years old.

well my goldfish has taken a turn for the worse. As of yesterday (Monday) the red bump has gotten big again (it had decreased in size) and now beside it is a black dot. The fish is also sitting on the bottom of my aquarium. He will swim up to grab some food but then goes back down and sits very still - almost looks like it is gasping for air as its mouth is opening and closing at a very fast pace. I have just completed 7 days on Melefix. I went to a pet store today to see if I should get an antibiotic like Maracyn and they told me that since there is already Malefix in the tank I shouldnt mix in any new drugs. I was instructed to do a 25% water change then do another cycle of Malefix (7 days). I question this. My fish is worse now after 7 days. Do you not think I should be trying a different medication or do another dose of Malefix.

I'm sorry to hear this.
It does sound like some kind of illness now and I feel you should try a different medication.
Melafix is a natural remedy and I've used it along with medications before.
I'm amazed everytime I go into the fish store and hear all the bad advice being given by employees. You were right to question their advice.
It's time to try something different.
I'd look for something that treats fungus and parasites.
See if any improvement after 3 days of treatment.

I hope you don't lose the fish, but sometimes even the best efforts are unsuccessful. Please let me know how it goes.

I didnt get your reply until today (Thursday) so Tuesday evening I did a 25% water change and started with another cycle of Melafix. Fish bump does look better and the dark spot isnt as dark anymore - but he is still sitting at the bottom of the aqauarium lots. I am going to take your advice and try a different medication. Should I do another water change again before starting a new medication? Will medicating the entire aquarium for one fish harm the other 5? I would hate to risk losing them all. Any medication in particular you recommend? I have used marcyin before.

Mela-fix is safe to use with other medications.
I would continue using the melafix along with the medication you choose.

1) you could use Pimafix along with the melafix.

2) you could use a medication for gram negative infections like Mardel Maracyn-Two or Tetracycline along with melafix. (recommended)

It's probably not a bad idea to treat the whole tank because they been exposed to it already. The surest way (although nothing is for sure when it comes to fish illness) is to treat it early.
If your other fish aren't showing signs of illness, that's early enough for me.

I apologize for not getting back to you as quickly as I'd like, I've had a few really busy weeks. I hope the fish will pull through.

I honestly dont know what I would do without you!!! Thank you once again for all your great advice and for responding so quick to my messages! I am going to try one of the meds you recommended and I will update you on how it goes. I agree with you that it really is surprising how much the people that work in pet stores really dont know! Thanks again!!!

Ok tonight (Mon)...I am on my 3rd day of maracyn-two treatment. My one fish seems to be getting better as he isnt hanging out at the bottom of the aquarium much anymore. BUT ...tonight when I got home from work I noticed that my aquarium is VERY cloudy. It wasnt that way this morning when I left (I put the medication in the aquarium in the evening). NOW all 5 fish are hanging out at the top of the water and almost appear to be gasping for air! What should I do. I am thinking of doing a partial water change. I did do another treatment of Marcyn-two when I got home (even thought I really didnt know if I should have with the cloudy water)!