Black mark on Sunshine Cichlid dorsal fin

[Skywarn23]

I have a Sunshine Cichlid that has a black mark on its dorsal fin.   I have seen this before on a Venustus cichlid I had.  Overtime with the Venustus the black mark grew and permanently damaged the dorsal fin and then moved onto the body adjacent to the fin.  It kinda looked like a tumor once it started growing on the scales.  The fish did die, but I was unsure if the mark caused it.  Overall the fish seems fine.   I have done a ton of internet searches and have not been able to find anything to assist me in identifying and treating the condition.  No other fish in the tank have been impacted.  Thank you in advance for any help.

Edited January 2, 2021 by Skywarn23

[Colu]

From what I have read black patches of your cichlid  can by caused by  ammonia burn parasites or bacterial  what are your water parameters