I just noticed today that 1/5 of my golfish has a big bump on the side of it with red tones underneath it (the size of a big pimple!). I have 5 golfish in a 33 galon tank and the remaining fish look fine. The fish with the bump is active and eating as normal - no signs of distress. What could this be and what should I do about it?

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 there 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 shouldn't 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 every time 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 didn't 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 isn't 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 don't 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 don't 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 isn't 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 wasn't 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 didn't know if I should have with the cloudy water)!

The medicine will cloud the water. But it does not harm the fish.

Is there any chance that you may have done too many water changes?
Or over cleaned your tank/filter/gravel?
Do you have any water tests to check ammonia, nitrite, nitrate?
There's some pretty convenient 5 in 1 dip stick tests that are pretty useful for times like this to make sure water is good.

Do you have a bio wheel or bio sponge to house the beneficial bacteria? I can't remember if you've told me or not.

How does the sore look?

If your water has any ammonia or nitrite present in the water, you'll want to stop treatment until the nitrogen cycle has repaired its self. This too can cloud the water, but the medicine does in fact cloud the water.

It will just be good to check the water to make sure that's not what's causing them to sit at the bottom.

Do you have lots of bubbles going into the water?
You can add extra bubbles (oxygen) to the water by lowering the water line 2 inches below the filter. Kind of like making a little waterfall.
That's a good easy way to provide more air to your fish during treatment.
Give that a try to see if they perk up a bit.

I am going to purchase a home test kit to test my water but haven't done that yet. As of Today (Thurs evening) 4/5 fish are acting normal. The 1 goldfish (that was initially the sick one) has not moved from the bottom of the tank for 2 days. His body is now swollen and looks sort of like a pinecone. What do you suggest I do? I have still be medicating with Marycin two - but no improvement (5 days now - today day #6).

Oh no this isn't good.
He has dropsy.
Dropsy itself is not a disease but a symptom of any number of fatal diseases.
I'm so sorry, but this is fatal. When he dies, the other fish may peck at him and contract the disease in a fatal way as well.
It would now be best to separate him from the rest of the fish.
Continue the treatment for the rest of the remaining time on the other fish even though they are not showing signs of illness. This way it's being treated before it's too late.
I'm so sorry.
You're other fish will more than likely be OK due to your good efforts in trying to treat the sick - the others are being treated early.

Do you have another tank, fish bowl, or divider?
Another tank or a fish bowl with an air diffuser placed close to the top so that the moving bubbles don't push the fish around but give oxygen to the water would be best.

Only a couple hours had past since I sent you my last message when I went to check on my fish and my sick goldfish had died. So the remaining 4 appear healthy and active with no signs of anything yet. Hopefully he wasn't in there long enough for the others to peck at him. Do you suggest I treat the entire tank still? At what point do you recommend a water change? I still plan on purchasing a home water test to make sure my levels are OK. Thank you again for all your helpful advice.

I'm sorry to hear that.
It would be good to make a partial water change. No cleaning, just removing and replacing about 10% of the water.
Treat with melafix for 3 more days as a disease preventive.
Then replace activated carbon and care for tank as usual.

Be careful with antibiotics! - they can really upset the natural balance of good bacteria in the water, and then you get something called a "bacterial bloom" where there is too much bacteria for a bit and the oxygen gets depleted. I killed a fish this way. I would recommend not taking drastic steps. Instead just do a water change, add a little aquarium salt and see how that goes. Regular water changes keep the tank healthy. No one warned me that antibiotics can ruin a tank and it looks like you had the same problem, so just a warning to everyone out there - repeated rounds of medication will mess your fish up.