White "cyst" on oscar's fin, what is it?

[HenryC]

Have you tested your water?

Yes

If yes, what is your ammonia?

0

If yes, what is your nitrite?

0

If yes, what is your nitrate?

15-20

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?

41-50%

How frequently do you change your water?

Every week

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.

My oscar has had this for a while now, what is it and how do I treat it?

 

[Jexnell]

To me it looks like a break/sprain in that particular ray of the fin. Gets bent to far and they get fractured. In time will heal back to normal.
Here you can see my Amphilophus Saggitae had one.

Now its gone.

Here one on my Oscar
That in time healed

 

[Deadeye]

I agree, just looks like slight damage. Whether from hitting a decoration or fighting another cichlid, it happens. I’ve seen it in my fish plenty of times. It will heal soon.