Id strongly recommend getting some of the bottled bacteria such as API Quickstart. Then id do a big water change and give the tank a double or even triple dose of it. If you cant get it until tomorrow then still do a big water change today.
This isnt terminal yet but you have to act quickly and keep on top of it.
Good luck, bit of a lesson learned for you, stabalise the water and get the tank cycled then worry about the fish stocking after that.