What can this growth be?

[rmkblades]

Have you tested your water?

No

If I did not test my water...

...I recognize that I will likely be asked to do a test, and that water tests are critical for solving freshwater health problems.

Do you do water changes?

Yes

What percentage of water do you change?

71-80%

How frequently do you change your water?

Every two weeks

If I do not change my water...

...I recognize that I will likely be recommended to do a water change, and water changes are critical for preventing future freshwater health problems.

It looks like a red meaty growth that shrinks sometimes, but then reappears. Is it a parasite? Tumor? Thanks I advance.

 

[rmkblades]

Ammonia 0
Nitrites 0
Nitrates 10

 

[Deadeye]

Has it ever gotten larger than the current size? Looks like an abscess, I wouldn’t be too concerned unless the fish is reacting poorly.

 

[rmkblades]

Has it ever gotten larger than the current size? Looks like an abscess, I wouldn’t be too concerned unless the fish is reacting poorly.

Fish is acting totally fine. It's been there for months and shrinks to almost nothing and then gets to the size in the pictures at its largest. Then shrinks again.

I appreciate your help!