Fish HELP!!? My fish are getting sick!!?

Question

So about 3 days ago my big angel fish started acting weird, floating around, not eating, things like that. Eventualy he ended up in the bottom of the tank, not having the strength to swim anymore but is still alive i took him out and put him in a seperate container with some stress zyme in it since thats the only thing i have. Then this morning when i woke up my black ghost was doing the same thing, floating on his back, barely moving. They're both still alive but i dont know what caused this!! I have a 55 gallon tank water around 80 give a degree or 2, i have a catfish type thing (not sure exactly what it is, but about 3 inches long with long whiskers), 3 neon tetras, the angel fish, and the black ghost. My water's fine with no amonia and such, but the nitrates are around 40 ppm ive been working to get them down with water changes. HELP i dont want to lose my 2 fish!! They're still alive but just barely!!

Answer 1

sounds like swim bladder problem sinks to the bottom unable to swim or floats upside down or near the top get a treatment for swim bladder made by inter-pet it will destroy the bacteria which cause the infection but i would do the  treatment to all your fish as u said 2 of them have it already it is best to do all so it will prevent them from getting ill too hope this helps u out and good luck