I am so mad right now it isn't funny. Everything with my tank was going smoothly. The Cory's adjusted well to the addition of a male Betta and the Betta had no issue having other fish with him. Yesterday my apartment complex did maintenance in the unit next door and it filled my unit with this acrid chemical smell. Other than giving me a migraine everything still seemed fine. The smell continued into today and when I came home from work I noticed one of my Cory's floating at the top of the tank and having rapid gill movement. There was a light foam around the edges of the water and the chemical smell seemed to have been absorbed into it. I quickly did a 33% water change and treated with API Stress Coat +. I then removed the betta and am monitoring the Cory's since both were having rapid breathing and seemed paler than normal. Any advice would be great since I have no clue what else to do. The water test showed a nitrite spike but I currently only have strips so I don't really know a number.