did you remove the filter? If so I don;t think you can get nitrite or nitrAte unless you have a filter running.
But here is inf on nitrite poisioning anyways
Nitrite poisoning follows closely on the heels of ammonia as a major killer of aquarium fish. Just when you think you are home free after losing half your fish to ammonia poisoning, the nitrites rise and put your fish at risk again. Anytime ammonia levels are elevated, elevated nitrites will soon follow. To avoid nitrite poisoning, test when setting up a new tank, when adding new fish to established an tank, when the filter fails due to power or mechanical failure, and when medicating sick fish. Symptoms:
Fish gasp for breath at the water surface
Fish hang near water outlets
Fish is listless
Tan or brown gills
Rapid gill movement
Also known as 'brown blood disease' because the blood turns brown from a increase of methemoglobin. However, methemoglobin causes a more serious problem than changing the color of the blood. It renders the blood unable to carry oxygen, and the fish can literally suffocate even though there is ample oxygen present in the water.
Different species of fish tolerate differing levels of nitrite. Some fish may simply be listless, while others may die suddenly with no obvious signs of illness. Common symptoms include gasping at the surface of the water, hanging near water outlets, rapid gill movement, and a change in gill color from tan to dark brown.
Hi Orsini, so all this happened while you were on vacation? That does make sense then that it could be ammonia poisoning. I know you wouldn't have let it happen if you had been there. Too bad we can't take our fish with us on vacation, huh?
At this point, the effects could go either way. He might recover or he might always be like this. :(
If he has trouble rising to the surface to breathe, you can lower the water level as much as necessary to make it easier for him. You can continue with the AQ salt for up to 14 days. Its main effects will be to help him create slime coat, which will help to fight off infection. There is no way to actually treat ammonia poisoning, unfortunately.
Keep his tank dim and quiet and continue with partial water changes as often as you feel necessary, replacing the AQ salt that you remove with each water change. So if you take out say, 1 gallon of water, replace 1 tsp of salt. Don't replace all the salt if you haven't taken it all out because the salt doesn't evaporate out of the water and so it would just accumulate to a toxic level.
Good luck, Orsini, and keep us updated on how he's doing.
If it's anything other than ammonia poisoning, it would be internal bacterial infection or gill flukes. If it's gill flukes, the AQ salt and water changes will take care of that. Unfortunately, without other symptoms there's no way to tell if he has an internal bacterial infection or not so it's very hard to treat him for that. Your best bet is to stick with the AQ salt. Try and keep his tank at about 80 F too. I really hope the little guy pulls through for you.
I've moved him to a much smaller hospital tank with a heater. Still doing the AQ salt but haven't seen any improvement yet. Hopefully he eventually comes around... if this is how his life will be it's pretty saddening.
If he's eating, at least he has a will to live. I always worry when they stop eating. It could take him a while to recover. I imagine ammonia poisoning could be a lot like carbon monoxide poisoning so he might just need some time to regain his strength. Only time will tell. :/