Ok has that discus allways had the red mark? Or is it from the illnesses? Better pic would help. Are you saying you have 10 discus in a 30g or just 2. How big is your main tank? And what’s in it now. Your ammonia is a problem keep water changing. How long hav3 you had these discus and where did you buy them.
Had more ? But I keep getting logged off. I’m new here so I guess you only get so much time to answer.