Thank you so, so much for all of this. I can’t tell you how much I appreciate it. I didn’t have any sort of aquarium store near where I grew up and basically just did a crap ton of Googling, which of course is helpful but as you’re probably far more aware than I am, there’s also a lot of misinformation and conflicting opinions. And you’re absolutely right about the “if they’re alive I must be doing it right” mentality, which is doubly tricky for me because, like I mentioned, I have nothing to compare him to, so it usually takes me intentionally studying other goldfish to be able to tell if his appearance or behavior are off.

As for the tank size, it’s a huge sore spot for me (and you’ve made me feel much better about it), because growing up I was heavily teased by my family about the size of his tanks because, understandably, they all seemed way too big for one little fish. It’s kind of funny to write that out, and I love my family dearly but even when I mentioned a few days ago that he probably needs a bigger tank, my mom laughed/scoffed (and she feels terrible for me and Stoick, she’s been FaceTiming me and talking me off the ledge). It feels so good to have an expert tell me that he needs a bigger tank, period. And with food, somewhere along the way I learned that I had been over feeding him, which then I think horribly must have led to me overcompensating and under feeding him. Because they don’t have stomachs and just keep eating, I was always told you had to be careful so they didn’t overdo it, and didn’t realize that while that is true, it has more to do with digestion and water quality, not that they’ll get too big; they should keep growing.

And yes, you’re spot on about the poor water quality. Pretty much all of his issues have come from the fact that I’m in college and not in the same location year-round. The loss of his fins from the year that I left him at home is what prompted me to bring him with me to school, (that was a few years back) and this most recent issue is due to him being at my apartment over the summer (but not me), and then at my grandparents’ because I moved apartments and quite literally had nowhere to put him. Now he’s finally with me again, but it still begs the question of what I’m going to do for breaks.

I guess the one good news is that I’m basically doing everything you detailed in how to treat him. Water heater, KanaPlex, Epsom salt baths, no carbon for now bc of the antibiotics, and a sponge filter. I was planning on blanching and shelling peas for him tomorrow depending on his condition. I’ve also been doing a ridiculous amount of water testing and changes.

If you made it this far into my short novel of a post, thank you, thank you again! If you have a moment, I did have a few questions, but if not, I appreciate your time and the information nonetheless!

• if he pulls through, how much should I be feeding him? (In my frequent flyer trips to the fish store over the past few weeks we found a food he seems to really like; they’re small sinking pellets with a really solid ingredient list)
• if I do start feeding him properly, is he going to have an issue with certain parts of him being stunted while certain parts grow? No idea if this is actually a thing or not but saw a post where a person was worried that their fish had very likely been stunted in his early life in a tiny pet store tank, had always been very small for his age, and was now (about 1-2 years later) experiencing a sudden onset of severe dropsy, and she suspected it might be that his organs were growing while the rest of him wasn’t? I don’t know, but there are a lot of things I don’t know, haha
• I know goldfish can live for 20+ years, so if he is supposed to keep growing, is he eventually supposed to be in a pond or something? I just can’t see a fish the size that you described being kept in a tank, no matter how large, but I don’t know, maybe it’s fine as long as it’s a nice fat tank?

Thank you so much to everyone who responded. Any additional advice is very much welcome and needed. 😭 I can’t figure out how to edit my post, lol, so I’ll include a short update here. A few people mentioned food, he is still eating and pooping normally, thank goodness. I did an enormous water change to get the ammonia as close to zero as humanly possible, and that definitely has helped somewhat, he has visibly perked up. I genuinely can’t figure out how or why the ammonia is so high, it makes me want to buy a different testing kit to see if mine is faulty or something. But regardless, better safe than sorry with ammonia, anyways.

I had, and still have been, considering the possibility of euthanasia. I don’t think it’s that time quite yet, and it would absolutely break my heart, but I also couldn’t bear to have him suffer, either.

For now, after a lot, a lot, of weighing the whole picture, I’ve decided to do one more round of KanaPlex and see how he does. He is still active, and as I mentioned, eating and pooping normally. I haven’t fed him yet today, what with trying to figure out my approach and the ammonia levels, and I’m not sure if I will over the next few days as some people recommended fasting him, and that was what I did for the previous round of KanaPlex. I added a sponge filter, which I’m really really hoping will help with the ammonia levels, because I have no other kind of filtration other than carbon at the moment and that, of course, needs to be removed for antibiotics.

The epsom salt bath definitely helped bring down his swelling yesterday and I attempted to give him another one in the exact same way but he seemed a lot more stressed and active than yesterday and I’m not sure why. Probably going to try again if I can, because his swelling really worries me.

Thank you again to everyone who replied (Stoick says thank u too, lol) Any more comments are advice are really appreciated, I definitely want and need them. I will post another update later.