Clownfish sick???

[Bray84]

Hi so after I fed my fish was checking my fish and notice the bigger clown had scare like mark/see through line behind the right fin few mm away from the gills and wondering if its a Parasitic Infection or anything bad. All test are fine but nitrates sit between 10-20ppm, eats like a pig and think its been there awhile so any info would be great

 

[Datreeferman]

My clown has the same thing on his face, I don't think it's a parasite. I've had him for 4 months now with that mark on him. He should be just fine