Big red dot on my fish. Not sure how to treat him

[loveno1]

Hello everyone, this morning I noticed something weird with my flowerhorn. There’s a big red spot on his tail. It kind of looks like his flesh is bulging out through an opening or something. Not totally sure what’s going on. Anyone know if this might be an injury or some kind of disease? Also, what kind of treatment should I use? I’ve attached a few photos for reference. Really appreciate for any suggestions.

 

[phreeflow]

Probably viral lymphocystis. Self limiting and should go away on its own. May cause a secondary bacterial infection so keep your water clean, lower temps, and keep an eye on it. If it gets much worse, you can treat the secondary infection but you shouldn’t have to normally

 

[danotaylor]

I would add salt in addition to keeping clean water to reduce bacterial counts in the water column and help prevent secondary bacterial infections. Replace the salt to maintain a 1tbsp/2gal with your water changes for 2 weeks.
I use this water softener from Home Depot, it’s 99.8% pure sodium chloride and much cheaper than gimmicky “aquarium salt”