So i just cleaned my goldfish tnak and did a larger than usual water change. And it fucked up my tanks eco system long story short i have a sarsa comet breathing extrememly heavily and not moving at all. I currently have him in another more established tank with an airstone next to him. What do im wiling to do anything
shouldn't have killed your fish. time frame between water change and death? if you use an unusual dechlorinator and use too much it can drastically drop the O2 level. I doubt you had that one. If you used drastically colder water you might have problems. buy some test kits ammonia, ph, nitrite and nitrate. its hard hard to seriously help people without test result. even then if you really know what you are doing but need someone who is some fish expert help they are going to want to know the test results too. sorry for your loss. my best guess is you didn't use dechorinator.
oh man probably the late 80's everyone i knew just filled a trashcan and left it in the sun the day before. but then can chloramines. and everyone got scared into buying a new product. I have become convinced its necessary. I have seen no information to the contrary.