Sick Green Severum

[cyberbeer65]

Can anyone tell me what is going on with this fish?

Thanks in advance.

 

[the loach]

How did this develop, did it grow larger, was it suddenly there,....

 

[cyberbeer65]

How did this develop, did it grow larger, was it suddenly there,....

It's been there for about two weeks.

 

[FreshyFresh]

Water param readings?

Any new additions to the tank?

 

[cyberbeer65]

Ammonia 0, Nitrite 0, Nitrate 40.

No new tankmates in two years.

 

[FreshyFresh]

Has it changed any?

My big green sev can get similar marks on it when it decides to be a jerk and bully it's oscar tank mate. This pair has been together since 2013 when they were babies.