What is this on my fish?

[Jonnypro]

It's the only one that is like that in the tank. I have a55g fresh with all types of fish in here. The water tests fine and I am at a constant 79.6 degrees.

 

[Jonnypro]

It seems lik there might be a little fin rot but also near the back fin there is like build up on the scale and part of the fin.