Short body flower horn?

[philipraposo1982]

Was that picture taken right after a water change?

 

[Dr. Sugandh]

Was that picture taken right after a water change?

Yes

 

[Dr. Sugandh]

My short body flowerhorn fish developed a pimple like wound its size increased and after one week it looks like this( look at the attached pic). What is the disease and how to treat?