Well i have a problem suddenly appeared with many couples, some of them were breeding fine before, they suddenly stop feeding there chicks at there middle nest age, something about 16 days old or something, they just stop feeding them, it happened with many couples, any ideas about the reason and solution? thanks so much.

It is has happened with multiple pairs, then something in the environment has changed. It may be rodent-based, or even insect-based. Look for signs of pest infestation.

Are you colony breeding...Lots of pairs in an aviary with nestboxes ? If so, others can affect budgies access to their chosen nestboxes and their ability to get back to their chicks and feed them. Also as Dave suggested..........rodent activity will drive budgies out of their nestboxes. Also, budgies going out of condition during the raising of babies. Lack of food. A lot of people think there is plenty of seed when there is only husks and some people do not anticipate the amount of food feeding parents go through.

 

More info needed please

Yes, check the seed dish and make sure there's plenty of seed - parents feeding their chicks go through a lot more seed and water than normal and if they run out they will stop feeding.