Black paradise fish unwell? Urgently want some id so i can treat my silly dude

[sned]

He seems fine in how hes acting but this has appeared overnight and has me concerned about his safety. Hes in a brand new cycled and dechlorinated tanm w hiding spaces and cover and he was bought only a few days ago

 

[Andy Sager]

He seems fine in how hes acting but this has appeared overnight and has me concerned about his safety. Hes in a brand new cycled and dechlorinated tanm w hiding spaces and cover and he was bought only a few days ago

That looks like either a bruise or an early infection. If it's a bruise, some salt ( 1 tablespoon per 3 gallons of water) can help it heal. ( Make sure nothing else in the tank is sensitive to salt. ) If it continues to get worse with the salt, it will need to be treated with an antibiotic. Your water parameters will dictate which one(s) you should use.