'Out, Dammed Spot!' (William Sharkspeare)

[Tanked]

This otherwise healthy Bloodfin has developed a large spot. I assume it to be some sort of hemorrhage or injury, but I'm hoping otherwise. I don't know when this first occurred. These fish are very active and it's hard to keep track of just one. What do you think?

 

[Colu]

Look like a bacterial infection  I would treat with kanaplex and add a small amount of aquarium salt 1 table for 5 gallons the salt will aid Gill function and add essential electrolytes and at that level won't harm your plants