Thank you for your patience. Diarrhea in birds has many possible causes. It can be caused by many different conditions and by parasites. Bacterial infections are common causes. There are a number of different bacteria that could be responsible. The following site has more information on this:http://www.cockatiels.org/articles/Diseases/ecoli.html
Diarrhea can result in dehydration, which can be fatal. I think your best decision would be to see an avian vet early next week. You should take along a sample of fresh droppings in a plastic bag. This link will take you to a directory of vets:http://www.birdsnways.com/birds/vets.htm
Because there are so many different possible causes of diarrhea, home treatment isn't likely to be effective. You really need to have a vet diagnose exactly what is wrong in order to start proper treatment. The remedies you can buy in pet stores are never a good idea. Fro one thing, they're usually added to the water, making it taste bad. The cockatiel simply stops drinking, which greatly increases the risk of dehydration. Most of those remedies have been stored for a long time. They're likely to have deteriorated to the point that they won't work at best, XXXXX XXXXX dangerous at worst.
Diet is the single most important factor in keeping our birds healthy. Many people still feed a diet consisting mostly of seeds, but recent research has shown that an all-seed diet is not good for cockatiels. Pellets, supplemented with various fresh and healthy “people foods,” along with a few seeds make up a healthier diet. Birds that are fed mostly seeds tend to develop fatty liver disease, tumors, and other health conditions, so that could be a factor. However, since your bird is used to eating mostly seeds, you’ll have to convert him to pellets gradually. The following two sites are where you can get reliable information on feeding and care. The second one has a section on converting from seeds to pellets. http://www.4animalcare.org/birdshttp://www.cockatiels.org/ownersandenthusiasts/converting-seed-junkie-to-pellets.htm
If you have more questions about this, just let me know by clicking on REPLY. I hope your cockatiel recovers quickly.
(If you find my answer helpful, please click on the green ACCEPT button. Thank you.)