Under the skin bleeding?

[RobVG]

I have 2 goldfish. One is a comet and the other is a fancy. I've had them for 10 months.
Over that time, the comet has occasionally had swollen areas that look like there might be blood under its skin. It's happened 4 times now and usually goes away in one or two days. He just got over it but it appeared again 2 days later on the other side. The fancy fish has never had this condition.
What could it be and what can I do?
Thanks in advance.

 

[Colin_T]

Pictures of the fish and one showing the entire tank?

What are the tank dimensions (length x width x height)?
How long has the tank been set up for?
What other fish are in the tank?

What is the pH, ammonia, nitrite & nitrate of the water?
What sort of filter is on the tank?
How often and how do you clean the filter?

How often do you do water changes and how much do you change?
Do you gravel clean the substrate when you do a water change?
Do you dechlorinate the new water before adding it to the aquarium?

What do you feed the fish?
Do you add anything to the tank when the fish get the red sores?

 

[RobVG]

Have you ever had a fish with the described condition?

 

[Colin_T]

I have seen fish with all sorts of health issues but I need a photograph of yours to identify the problem. I also need the questions answered so I can make a more accurate diagnosis.

 

[RobVG]

Tank: 23×11x11" bowfront
Set up 4 weeks ago.
2 fish
Air driven undergravel filter- vacuumed every water change. 2 uplift tubes.
25% change every other day, recent 50% change.
Tetra Aquasafe water conditioner.
Food: Tetra goldfish flakes and Tetra Pond Sticks

Currently not testing water, kit on it's way.

Again, this condition has only show up 4 times in 10 months and clears up in a day or two. The fish was in a 5-g tank for 9 months and it showed up twice in that one
The other fish has never been afflicted.

 

[Colin_T]

Does the water have a milky cloudy appearance to it or is that the picture?

The fish looks like a white or calico shubunkin and they can show red or pink patches under the skin as part of their colouration.

The white patch sticking up from the skin looks like excess mucous covering a wound. It might have got caught up on the tree root or driftwood and scratched itself.

Need a clear picture showing the whole fish from both sides to be more certain.

 

[RobVG]

It's looking much better today, almost gone.
I did some searching online and the description and pics of "Red Pest" was the closest match. It's a bacterial infection cause by stress induced low immunity and usually brought on by water quality issues.