How to stop budgies biting their cage? 

I read somewhere that it has to do with iron deficiency? I haven’t purchased those blocks to Chew bite but they don’t bite if and are afraid of it even though I move it around. I was told by my vet to not give them vitamin drops into their water bc of possible bacteria and I am not sure what to do. 

the cage I purchased is white so they bite the paint off and it just leaves exposed metal. I haven’t had the cage for even a year but it looks bad bc of the paint they peel. They used to bite the paint off my wall but I covered it up with a tapestry to hide their spot and before they would bite on my calendar, bag, newspaper, and tiny bags so I had to hide those or remove them from my room. Is there anything I can do? I keep buying wooden toys and perches but they mostly seem interested in just biting their cage and it looks bad already. 

I move their toys around, they get good amount of sleep, they eat pellets and sometimes millets and seeds as treats they have a lot of water, and I let them free fly in my room, I play with them/talk to them/play them music, they are always cleaned when needed, and their cage is deep cleaned every day. I am not sure what to do anymore as this has been going on for the past couple of months but it’s gotten worse these past two. 

I am thinking of purchasing another cage but these are costly and hard to set up 😭 and I really like the white cage look as it makes the room feel bigger but I think I may have to get a metal type of color but I have a feeling they will still bite. 

(I have six birds, and it’s three that do it but mainly two, I have shared images showing the bites of the peeled paint, it’s not all of the cage it’s mostly inside where they sit on their perches. They do bite some of their wooden toys but not as much as the cage. I try to break the habit by moving them but they still go back to doing it when they think I’m not looking. I am scared of them getting that toxic metal thingy) 

Please share any suggestions I greatly appreciate it! 

How to stop budgies from biting cage bars