Welcome to the forum and sorry to hear your zon has been sick. Seeing you live in Maryland, just curious if you live in the DC area? Parrots have very sensitive respiratory tracts, and some are more sensitive to things like air pollution than others. Wondering if Hollywood may be being affected by more than just seasonal allergies? Do you run an air purifier in his area? That may help whether it's the air itself or a seasonal-type allergy.
I have used colloidal silver before on my BFA, but not for allergies. I've used it maybe 3 or 4 times when I noticed he had a little runny droppings or sneezed a couple more times than he normally would, but it is a type of antibiotic, and thus will not help anything that is not bacterial in nature. I administered by putting 2-3 drops in his water dish. And even though he seemed to improve, I can't be sure it did anything at all as I had not taken him to an a-vet those times for proper diagnosis, water dish is a poor medication delivery method (he may or may not drink and who knows how much he will drink) and never knew if he was actually sick in the first place (just more of a preventative thing). PLEASE KNOW when you do home treatments there is ALWAYS a risk your bird has something else going on or the treatment will be wholly ineffective. I would ABSOLUTELY NOT administer colloidal silver long-term (for more than a day or 2), I would keep it a diluted dose (2-3 drops per cup of water) and would NEVER administer in a direct fashion (i.e. with a dropper into the beak). You also ned to use a stoneware or plastic dish with CS, as a metal dish will negate any affects it may have. Remember, silver particles can build up and cause issues of their own, so unless you are under the advisement of an a-vet, I wouldn't give it for more than a day or 2 to see if it helps.