This should be moved to the Emergency Forum, but anyway....
The course of action depends on what type of fish and plants are in the tank. I would recommend raising the temperature to 86-88 degrees, and add about 1tbs of salt per 5 gallon of water. But depending on the species of plants and fish, this may do more harm than good.
So repost in the Emergency Forum with a complete list of fish, and indicate if there are any live plants that are worth keeping.