I was thinking we had it figured at five teaspoons per gallon, it surprized me to see 2 1/2 Tbs. I like your math better, that package doesn't make very many gallons. It should come in a bucket, not a packet, especially since it is suggested to be used seven to fourteen days.
It isn't the dreaded P word. It looks like it is irritated and a little puffy. No drainage or weeping, no nasal discharge, perhaps it is an allergy thing. I would think there would be some of the normal runny eyes and nose if it was bacterial. Have you opened the eyelid to look at the eye?