My Fish Died

[Blue2000]

Beginner in dead oranda: had this and his friends for 3 years and recently he caught a fungal infection and was cured. Then he started not floating and I treated him for swim-bladder but he didn't float easily again and seemed unable to open mouth. Took him to the vet, water tested, poo tested, mouth opened, nothing wrong. Except the fish swam less and less and now died. What could possibly have gone wrong? Thank you

 

[Fahn]

Beginner in dead oranda: had this and his friends for 3 years and recently he caught a fungal infection and was cured. Then he started not floating and I treated him for swim-bladder but he didn't float easily again and seemed unable to open mouth. Took him to the vet, water tested, poo tested, mouth opened, nothing wrong. Except the fish swam less and less and now died. What could possibly have gone wrong? Thank you

May I ask his tank size, how many other fish in the tank, and the water test results? If any of these are ruled out, you did everything you could... sometimes fish just get sick and die.

 

[Blue2000]

May I ask his tank size, how many other fish in the tank, and the water test results? If any of these are ruled out, you did everything you could... sometimes fish just get sick and die.

Thank you. it is three little fish in 30 gallons. Air stone, filter, ceramic media. Was told to add a pinch of salt as disinfectant. The story spans over two months so the results vary slightly but always ok. Last time I had a good look at him changing water his skin looked transparent and his insides dark and poor thing was so heavy he just flopped. Alien invasion?
Resign to mysterious circumstances?