Fancy goldfish overnight illness

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Dec 26, 2023
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Hello everyone. I am hoping I can get some help with an illness I found very suddenly. Before I go on to explain the issue at hand, I have a 30 Gallon tank, the ammonia and nitrites sit at 0, and the nitrates usually hang around 20-40. The tank heater is set to 74. I know the nitrates are on the high end and that's why I have been battling that black algae for awhile. I am doing regular water changes. The problem is I need to switch to pellets from flakes but both of my fish have trouble seeing the pellets before they sink between the rock substrate. But that is another problem for another day. (probably switching out the substrate when work dies down.) Also to note I have only one other fancy goldfish in the tank that has no symptoms. No new fish have been added for at least 6 months. the newest addition is the current sick fish, and before that, the only other fish that's not sick about 18 months prior than that. No new plants at all.

Also please note that other than the telescope fish's new white dot illness, nothing to me looks out of the ordinary from what he has always looked like. He has always had a semi translucent body especially around his gills and butt. This is the first time he is sick. The other fancy has never been sick in the 2 years I have had him. However, if anyone thinks I am missing another symptom please point it out.

On Sunday the 24th I noticed a weird growth looking thing on his back right side. It took at most 2 days to form. The last couple of days were crazy with Christmas coming fast so I didn't get to watch the fish as much as usual. I attached the best pictures I had below. It is only one spot on his body. It looked like a red circle with a white center. The red circle was raised up, and the white center looked either like puss/fluffy and stuck out into the water pretty far. He was behaving normally, maybe a little agitated (maybe I was projecting). He didn't seem to be trying to rub up against anything and was asking me for food like usual. In the picture he was doing his usual scavenging for food, albeit maybe a little more forceful than usual. Now at this point to me it looked infected and possibly had fungus so I added API E.M. Erythromycin, Fin & Body, and general cure to the tank. While I am typing this I am still treating the tank with those medications. for the general cure I only had enough for 20 gallons so I lowered the water level in the tank for the first dose. The tank is currently back to the full 30 gallons.

On Monday the 25th the red circle started to get less raised and faded in color. The white center was half as long and no longer looked like puss/tufty. He seemed a little calmer like his usual self. I took a video of this day. They are both looking for the food they did not receive yet.

On Tuesday the 26th (today) The red circle is no longer raised, and is almost completely faded to his normal color, but the white center is still there. It is slightly less than half the original size and looks firm.

I have looked around the internet a lot, but I can't find anything that matches what I am seeing. It seems to be getting better but something tells me that white center might end up being a problem because it hasn't really changed as drastically as the red circle. Any help would be greatly appreciated. I don't want to lose my little guy.


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It could be the start of Goldfish Ulcer Disease, which is a bacterial infection that causes ulcers to form on the body and kill the fish. This is normally seen on goldfish that live in dirty tanks.

However, it just looks like excess mucous on a sore. The fish might have scratched itself or partially lifted a scale. Then it got a bit infected, or just sore, and the fish has produced excess mucous over the wound.

Normally treatment would include clean water and maybe some salt. Clean water involves doing a big (75%) water change every day for a week or two. Try to gravel clean the substrate when you do a water change.
Make sure any new water is free of chlorine/ chloramine before it's added to the tank.

If there's no improvement after a few water changes, you can add some salt. You can add salt straight away if you like but since nothing new has been added, I would do a few water changes first and add salt if it's not helping. But you mention it seems better now so water changes should work.

Since you have already added medication, finish the course and monitor the fish.

The medications you used might wipe out the filter bacteria so monitor the ammonia and nitrite levels for a few weeks.


The fish have trouble seeing pellets because they are usually smaller than flake foods and their eyes are looking out sideways and on extensions. They will always have trouble with small foods. Flake food is generally bigger and easier for them to see. Plus it floats and that can help them see the darker flake against the light background of the sky (light).

Goldfish should have a varied diet and I fed mine with a bit of flake, then some frozen foods like marine green (prawn, fish, squid and spinach blended up), various other frozen foods like brineshrimp, bloodworm, daphnia, and sometimes live food like brineshrimp and mozzie larvae. They also got a lot of plant matter in their diet, most of which was Duckweed, a small floating plant that most people hate, but goldfish love.


Goldfish don't need a heater and will live in water that is just above freezing, right up to 30C (86F). You can have a heater in with them but have it set on a low setting so they have a few months of cooler water and then it can warm up in summer.

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