Half of Dovii's face is dark.

[qguy]

Have you tested your water?

Yes

If yes, what is your ammonia?

0 ammonia

If yes, what is your nitrite?

NA

If yes, what is your nitrate?

Na

If I did not test my water...

1. ...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?

31-40%

If I do not change my water...

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

This just happened overnight. Anyone knows what this is or what could be causing it ?

He stays in a 400g system, two tanks connected to a single filter. The other fish in the other tank, does not show any illness. 150g water changes every week. 0 Ammonia. I do not have any other test kits.

 

[kno4te]

Sometimes see this with injuries. Like hitting the glass or decor. Would watch and make sure the fish is eating and water is clean.