Brandon, I remember you saying after a day or two of having your cockatiel that he was pooping whole seeds. I said that it was possible your cockatiel had some sort of digestive problem, as that was not normal and the food should all be properly digested so that he would get the proper nourishment.
I also said to take him to the vet for testing and to have this problem addressed, because if this were to continue, your pet would run the risk of slowly starving... If the keel bone is too pronounced then indeed your cockatiel is too skinny and would need to be on a special diet in order to gain weight.
Not to mention, he would also need treatment to cure the digestion problem, if there really is one.