Goldfish ammonia burn or black smudge!! Please help!!?

So I’m just got back from driving all the way home from school and I go to say hello to my goldfish, Ernest/Happy/Bubbles, and I see my once beautiful and healthy calico goldfish has black ALL over his face, body, and fins. He’s not swimming much and is sitting at the surface of the tank gasping. I looked online... show more So I’m just got back from driving all the way home from school and I go to say hello to my goldfish, Ernest/Happy/Bubbles, and I see my once beautiful and healthy calico goldfish has black ALL over his face, body, and fins. He’s not swimming much and is sitting at the surface of the tank gasping. I looked online and it said maybe either black smudge or ammonia burn. I tested the ammonia levels and they were 0.5 ppm which isn’t good but is it really THAT much to cause something so severe? One of his eye balls also has some white like it lost coloration or something? I have NEVER seen anything like this and idk what to do. Before I even put anything down basically I changed some of his water using a dechlorinator, but considering I just drove for several hours and it’s 12:30 am there’s not much else I can do. My mom got him a new filter like 2 weeks ago and I checked it when I got home and she didn’t actually take the filter out of the plastic wrap so it wasn’t doing anything so I feel like that might be why he is like this. Is there something I can put in the tank to make him feel better? And how do I know if it’s black smudge? He’s not swimming much but it is late and idk how he’s been eating because I haven’t been home in a few months, although he does look a little slimmer. I attached some photos PLEASE HELP !
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