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 68į, 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.