He takes feed from a spoon actively and stops when his crop is full. I've ordered a scale
That's great
Just out of curiosity, is this a wild bird? You may want to look into a rehabber.
In the meantime, keep the chick warm. Warmth is important for chicks and the temperature should be kept as constant as possible to avoid problems in the crop.
Be sure the food you feed is 105F. No lumps, just like you would prep for your budgies.
I have no idea when these birds wean on average, so when the scale comes weigh him first thing in the morning on an empty crop, then feed 10% during every feed that day. You can give a little extra, but be careful not to overfill the crop.
Everytime the crop is almost empty, feed him again. Keep note of all the times and use this as a guide daily to know more or less when to check him and feed him.
Every day he will weigh a little more, so the food you feed will go up a small amount.
When it comes to weaning, you cn start offering adult foods (Steamed veggies, soaked pellets to start) once he is full of pins and some feathers opened ( this will still be some weeks away).
From there, he will eat less formule as he eats more adult foods on his own. When giving adults foods, water should be present to drink.
Here is a good article, have a read and save it for when you need it;
