he'll be fine for a little while without it, for now just do some water changes every day to start getting the water nice and clean. Then when you get the salt you can start that.
Do they have heater's yet? If I remember correctly that was something that you never got for them. It might help to invest in a glass thermometer as well to float in the water so you can regulate their temp better. Lower temps can also cause diseases because the fish's immune system slows down whereas with higher temps he speeds up to stay healthy and active