As a breeder, I use large quantities. of liquid and powder vitamins for wet food.
Lady Gouldian finch website has a lot of good powder electrolytes, liquid vits and probiotics Like Flourish, Energize etc and they are very helpful with making choices, as well as illness issues. I recently put our whole flock on energize for support from the summer heat stress.
I use Soluvet D-3 Breeder from Vetafarm. it is very expensive but Soluvet D is more reasonable for folks with small numbers of birds. Outstanding for breeding vigor. It takes continuous 6 months to show changes in vigor, so be patient if you use it. The D-3 in concert seems to be a major key.
I also buy Prime from www.FosterandSmith.com
vet catalog to be used in water or I sprinkle it on moist food. It has probiotics that I like as well as the usual stuff. I try to offer my birds alternative sources since they can not forage in the wild for things their little bodies need. The wild birds seem to have an innate guidance for what they eat for fuel or health issues. Amazing!!!
I also make sure there are extra sources of Vit A, Iodine, and digestible calcium. Vetafarm has a liquid calcium that is a good product. I keep Euca-mint with vit A and a tablespoon of apple cider vinegar per gal of filtered water for general use as it is good for respiratory and digestive support and has mildly antibiotic properties. I buy Euca-mint from Foys pigeon supply here in the US. Oil of Eucalyptus, and Oil of Anice are available in health food stores as it is some times hard to get Euca-
mint. These are great to use as a vapor therapy for budgies and I use it for me when my asthma is being frisky!! The aviary smells wonderful and the warm moist air is great for hatching babies!! A simple crock pot with a wire top for safety is less expensive than a vaporizer which may have teflon issues.
It takes awhile to absorb and develop your own nutrition program. I read a lot and practiced on the wild birds that visit my yard before I got the Budgies. I sort of put myself thru a course of home schooling to prepare for the budgie project. I have great mentors as well to call when I get in over my head!!!