Hello, this is Dr. Linda. I hope I can help with your question today.
I am sorry for your concerns about Titan. In all honesty, it would be best to try & have a vet come out & see Titan, especially with his previous medical problem & his age. A sudden green discharge could be an indication of several things, from a simple nasal infection, to something more complicated such as an infected tooth ( which may also be fractured ), guttural pouch empyema, sinus infection, or even cancer.
You can try the SMZ, the usual dose is 30 mg/kg once daily for 10 days ( 13,636 mg/ 1000 lbs ). But please only consider this if Titan is still eating well, & does not seem to have any other difficulties, i.e. not breathing hard, no cough, no blood in the discharge, & he is drinking adequate amounts of water.
I hope this makes sense & you find the information helpful. Please let me know if you have any additional questions or concerns.