Mystery Goldfish Disease

[shydust]

Please help! I'm fairly new to goldfish owning but not to fish owning in general. I've had some goldfish for almost two months now. There were 2 sarasa comets and 1 common (white) goldfish. This is long, but I'm hoping to be thorough so I know exactly what disease is occuring.

About two weeks ago one of my sarasa comets became sick. He would sit alone in the corner with clamped fins and wouldn't eat. By the next day I moved him to a hospital tank with a bit of epsom salt and he bent in a u-shape floating on his side at the top. He died within hours.

The second sarasa comet also started sitting in a corner right after the first died. He would lay (upright) on the gravel hiding behind a fake plant. Whenever I came around he would feebly attempt to swim but he had severe clamped fins as well. I fed him for the first two days when he had these symptoms and he would actively eat and chase the food but go back to the corner. Fearing swim bladder disorder I stopped feeding him. I treated the tank with melafix and did a 30% water change followed by a 20% the next day and 10% every day after that. After a week he also started floating at the top (not gasping, just floating upright). He, too, died within hours.

My final goldfish is a solid white common goldfish named Mr.Peaches. I fear that Mr. Peaches is also becoming sick because he has clamped fins and pop eye. Neither has become severe (yet) but when I observe Mr. Peaches where he can't see me he is always hovering about and inch off the gravel with his fins tucked in close. Whenever he sees me he starts swimming around and his fins will unclamp for a few minutes, then go back. I just noticed the pop eye two days ago but I couldn't be sure that wasn't the way he always is. He was also put on a no-food diet but once my second comet died I gave him a few small pieces of strawberry and a few more today. He loves them.

The problem is, as far as I can tell there is nothing wrong with the tank or the water. Mr. Peaches is now in a 10 gallon fully cycled tank with filter. He's all alone so there's no chance of overcrowding. Here are the water parameters. I've tested them multiple times the past week and they are always about the same:

Nitrates: 20-40 ppm
Nitrites: 0 ppm
pH: 7-7.5
Kh: 0 (this is currently being raised using baking soda, but it will take a while because I don't want the pH change to kill Mr. Peaches)
Gh: about 180
Temp: 65-70 degrees F
Ammonia: 0

Apart from adding baking soda (slowly) I've also dosed the tank with melafix and put in an aerator for extra oxygen (although the filter adds oxygen pretty well, I just want to be safe).
Mr. Peaches is NOT swollen, does NOT have pineconed fins, does NOT have red streaks (although it would be hard to tell if he did since he's white and you can often see blood vessels) and does NOT have frayed/discolored fins.

So, please tell me, what am I doing wrong?

[Tiari]

Stop adding things to the tank. I am not sure why you are adding baking soda to the water, when your Ph is already in normal range? Epsom salt shouldn't be used with fish, are you using that as a replacement for aquarium salt?

Melafix is also a questionable remedy, and the three things combined are likely doing a number on the fish.

I recommend several water changes over the next few days using nothing in the water but dechlorinator.

[bignellm]

Stop adding things to the tank. I am not sure why you are adding baking soda to the water, when your Ph is already in normal range? Epsom salt shouldn't be used with fish, are you using that as a replacement for aquarium salt?

Not answering for S.d., but I've heard of Epsom salt being used to help relax the muscles of the fish, so they can have a bowl movement--when they're impacted.

Clamped fins is a clear sign of distress. Usually with sickness or parasitical infections in my experience.

Other than that, Nitrates might be on the high side, a minimum 50% water change is in order to rectify that.

I would also stop adding things to the water. Without knowing what your dealing with, your most likely going to make matters worse.

But besides this, how large are/were your goldies and what were they housed in? Were they all in the 10 gallon?