Goldfish death

[Inkdork]

I have a 75 gallon tank that had 4 fancy Goldfish. The water parameters before I did a 60% water change last night were ammonia 0/0.25, nitrite 0, nitrate 5, temperature 68°, and pH 8.4.

Two days ago I noticed a little fluffy looking fungus on one of the ranchu's wen. It was kind of trailing off, very whispy looking. I started treating the tank with malachite green. I did a water change, treated the tank as per the directions (about 36ml for the whole tank) and repeated every 12 hours. At midnight last night, the ranchu looked a little bloated but I wasn't sure it wasn't my imagination. The tank was also salted with aquarium salt.

At noon today, the ranchu was extremely bloated, but his scales were flush against his body- no pineconing. He had no discoloration, and the fungal growth on his head has not gotten worse. His vent wasn't protruding. He was starting to bottom sit.

At 5pm, he had blown up even bigger, and was dead. His body was extremely heavy, and did not float, telling me this was a fluid retention issue and not gaseous bloat. I have no idea what caused this.

I had him for about 7 weeks and he was super active and healthy until 2 days ago.

Does anyone know what could have caused this? I feel awful.

[Autumnsky]

The first thing that comes to mind is a blockage like a rock or constipation.

Second I am wondering about any NitrIte spikes from ~ 2-3 weeks ago. Sometimes a fish can experience internal organ damage which can take a few weeks to progress to cause organ failure.

[Inkdork]

The substrate is super fine sand and the rocks in the tank are all a couple inches across. I don't think it was a water quality thing because I've been testing often both before they moved to this tank, and since. And I moved the old filters over to the new tank to get the cycle going.

His belly just felt like a water balloon when I scooped him up to examine him.

I'm freaking out because I don't want to lose any of the rest of them, obviously, but Tank was my favorite.

Eta he was pooping normal poops last night.

[Autumnsky]

Sounds like it could be kidney failure, but why... It would seem an infection, maybe causing swelling and blockage. A guess. I'm no fish doctor. There was obviously stress on this fish from something.

How long did you have him?

[Inkdork]

About 7 weeks I think? Maybe 8? He was the picture of health up until he wasn't.

Active, always begging for food, constantly trying to get the girls to spawn... Lol.

[Autumnsky]

How do the rest of the fish look? Was Tank's illness isolated? Really sorry you lost him.

Hoping to hear the rest are doing okay. Hope you are as well.

[Inkdork]

The others remained well and are still the picture of health. I have no idea what took Tank but it was bad. It's funny how much you can miss a fish.

[Autumnsky]

So true.

Very glad the others are good.