I’m very sorry that someone was irresponsible enough to sell you an unweaned chick. It’s even worse that they didn’t give you complete instructions and make sure you know how to feed it before taking it home. You should have been asked to come in several times for feeding lessons and not been allowed to take the bird home until you were confident with feeding it. Ideally the bird should have been weaned for you. I personally would take the poor thing back and get a refund. And then buy a weaned bird from someone else.
I can only help so much, not knowing the bird’s age, the brand of formula and how often it was being fed at this point. I can’t recommend anything specific because if I guess wrong, he could die. The formula needs to be mixed with the correct amount of water where it isn’t too thick or too thin. It has to be at the right temperature where it isn’t too hot or too cool. The baby can’t digest it properly otherwise. As for how much and how often, again, I can’t tell you for sure. The crop should be full but not too full – it should be like an under-filled water balloon and not tight. You should not feed it again until the crop is empty. If you feed it too soon, the new food can make the old food sour and this can cause digestion to stop and the chick will die. When a chick is sent home like this, probably more die than survive, and it’s a matter of luck that any do survive. He is at the age where he may refuse to eat for you. You can’t try to force feed him or he will get the food in his lungs and die. I’m not telling you all of this to scare you – this is the hard truth and it’s why this bird should not have been sent home like it was. I can only suggest searching youtube for videos that show how to hand feed cockatiels, and try to find videos made by someone who knows what they are doing.
As for weaning, it’s not as simple as giving the bird seed and water. To begin with, seed is not a nutritious diet for any pet bird. Loose seeds have almost no nutritional value, and any added vitamins are lost when the bird removes the hull from the seed. You need to feed him a nutritionally balanced diet such as pellets or our foraging diets. You should also offer soft foods like cooked brown rice with mixed, chopped veggies, dark leafy greens and some fruit. If he is picking around like he wants to eat, you can start offering these foods. He also needs a dish of fresh water. He needs a variety of foods available while he is weaning so he learns to eat a good diet from the start. Weaning can take several weeks while he learns to eat some on his own and is still supplemented by hand feeding. You can’t just stop handfeeding one day and make him eat on his own. Not only is he most likely to starve first, but if he does manage to survive, he will have behavioral issues caused by not being weaned properly.
I’m going to give you some links about what to feed when he is weaning in case you do keep him. If you keep him and can make it through the weekend, I would take him to an Avian Vet first thing on Monday and get them to help you with how to mix the formula and hand feed. I’m sorry there aren’t specific answers I can give you, but again, hand feeding isn’t simple and chicks can die with even the most experienced person hand feeding it. As someone who has never done this, you have your work cut out for you. I do hope things work out for the poor chick.
Bird Food Guide