Green watery droppings? (warning: includes photos)

[Ceku]

My male quail is sick for a week now. A month ago we lost one of his friends. She had exactly the same symptoms as him. He has droppings like
very watery green/yellow lines of mucus? not eating much, his crop is mostly empty, he is not so lethargic but mostly sits in the corner...
I went to the vet and used levamisole(for worms) and toltrazuril (for coccidia). Nothing changed.
a month ago, I have also used enrofloxacin (vet prescribed) for the quail that have died before and it didn't worked for her ...

I'm out of possibilities and so sad that i cant help him

Any idea what is his problemand how can i help him?

 

[casportpony]

Do you know how to tube feed? Do you have a food scale that you can with him on?

 

[Ceku]

Do you know how to tube feed? Do you have a food scale that you can with him on?

Unfortunately no I don't know how to tube feed. I tried to give him a little food by syringe but since I'm afraid it might go to his airways I stopped.
What do you think his problem is?