I was away from home for a day and on my arrivel I have noticed that my Sewellia lineolata has a weird looking red spot.
It is on the bottom side of the tail, a few mm away from the joint to the body. The spot is very red, a few mm in diameter and is also visible from the top side of the fish from each side of the body.
I have had the fish for about a year now, but I am ashamed to say that his river stream aquarium is still not ready

Could it be an infection from the new fish? Or maybe a disease that attacks Sewellia lineolata fish?
Would appreciate your help,
Thanks Planty.