Symptoms: The birds is lethargic and has puffed up feathers. Careful observations shows that it sleeps a lot. Diarrhea is present.
Cause: Can be caused from fluctuation in temperatures, damp environments, constant drafts. All of these are drivers towards lowering the birds general resistance thus causing it to get sick.
Treatment: Move the bird to quarantine. Ensure food and water is provided. However the birds will require antibiotics. (Terramycin for example will assist in recovery) You will need to consult your local veterinarian. Broad spectrum antibiotics are available off the shelf at local pet stores however this may not be the right action to take. Adding a probiotic to the water will in getting the good bacteria back in its gut.
Pet Bird Care Us magazine, Common Finch Diseases: Aries Munandi, June 2015