He gave me a large plastic bag full of powder formula to mix with warm water.
Do it like that, and the food will be too cold causing sour crop.
I boil the water to kill any bacteria, then make the food (to a thick pea soup consistency), and I stir continually until it has cooled enough. Check with a thermometer so you know when it is ready.
I find when I use freshly boiled water, it is easier to get rid of the bumps, whereas if I use cooled down water, it is harder to get th temp right and it doesn´t look like it has bumps, but if you try it, you will feel them in your mouth, and bumps are not good for chicks.
I don´t know about conures but when my birds (lovebirds) wean, it goes quickly from eating well, to eating little, then just rejecting the syringe completely - like it can happen in just days with some. Also worth noting, if the bird has been handfed for a while, they can turn into a bit of a goldilocks and if the formula is too thin or thick they won´t eat it.
3 days is a lot to put it down to settling in. 1 day yea ok, but not 3.
I´m actually surprised this chick is still alive - maybe he was eating something you left in the cage?
If he is eating foods now, then do not syringe feed this chick, it is too risky with your inexperience, the food not having the original packaging with instructions and the awful breeder who hasn´t helped you.. And please don´t use the rubber tube - that is for putting down a birds throat.
Offer many different types of foods and see what the bird will eat / what he likes. Avoiding avocados and aliums. I personally avoid tomatoes.
Try mashed sweet potatoes, sprouted beans, cabbage, kale.
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@iamwhoiam says, don´t stress out - your bird will sense that.
I´m really saddened that this breeder was happy to sell you this bird, knowing you didn´t have experience and not offering you any help, not even when you call back asking for help. That´s really crappy of them.
It sounds like you are doing ok now, Please let us know how you get on at the vet
@AviaryByTheSea I wouldn´t recommend a first timer using the microwave, it´s too easy to miss a hot spot. I don´t trust the contraption
@Hankmacaw Sorry, that was almost 3am for me