I'm sorry he is not feeling well.
Can you post some photos of how he is standing/sitting as well?
How old is he?
You mention bad nutrition? What do you feed him?
Tell us a bit more about his symptoms - is he lethargic, not eating/drinking, having a hard time walking/standing, any coughing/sneezing, runny nose, etc.?
Is he pooping- photos of the poop?
Check his crop to see if it's emptying overnight, look through his feathers for signs of lice and mites, inspect him for any injury and consider having a fecal float to rule out worms.
A bluish comb like that can be an indication that he is not getting enough oxygen.
Do what you can to keep him hydrated - you are in AU, I wonder if he is suffering from heat exhaustion? Some electrolytes for 24hrs won't hurt.
Keep us posted.