Well, I'm still experimenting
As staple diet they get a cockatiel and budgie mixed seed daily. They get fresh food a few times a week which mostly includes grapes, apple and those peppers you use in salads. They are very picky about anything else but I keep trying
Some of them also take berries and pomegranate but I don't have much luck with beans or leafy goods. I also haven't got anywhere with sprouted seed, cooked lentils or chop....but I will keep trying!
At first I also added canary seed with biscuits in and they LOVED all the small seeds. It has a few things not in the cockatiel and budgie mix so my idea was at least they were still getting variety!
I also add eggfood a handful of times a month for everyone even non breeders.
I gave them pellets for a few months until recently. I used the pretty bird daily select small biscuit like ones (size 1). Half take them and the other half don't. I don't mind them personally but was trying to get them on more fresh food since there is so much waste. my other option is get one of those seed recycler machines so I'm not constantly throwing alway uneaten pellets.
I haven't done it for a while but I also occasionally put aloe vera in the water, calcium or vitamin drops. If I have a bird comes to me rough I'll do it several times a week but then as the flock evens out to the same condition I just do it a few times a month. I also have brewers yeast I sprinkle on the food whenever someone looks a bit rough due to a moult or stress etc.
It keeps changing as I learn and as I am able to provide more. I spent about £1,000 this year on unexpected vet bills which is why I stopped buying pellets when they ran out and was pushing the fresh food more (my monthly pet food costs were like £100+ for everyone inc furries! Now I have it down to about £70 a month). This is also advised my by avain vet too. She wants me to drop everyone but the cockatiels down to around 1/3 seed, complemented by pellets IF they'll take it...but majority of the other 2/3 fresh food and basically to just be persistent with them! And to convince myself they wont starve to death as long as they have their 1/3 seed but that they will eventually get hungry enough to eat the other stuff...but I have to put it in the established food bowls so that it can be recognized as food
I also moved several into an indoor avairy and the others have decent sized cages...not huge...but enough to do a short flight one side to the other. This helps keep them lean and happy
however the avairy ones do get scraggy tails from running up and down the wire... oh well...