It depends on the size of the container. It's 1 tsp to a gallon so if your container is bigger or smaller than that, just adjust the amount.
No, at first the eye maybe slightly bigger or not bigger at all. He might get a white ring around the eye, where the eye meets the head. This is also a sign of popeye. If left untreated it may get huge and even actually pop D:! Usually if one eye is bigger it is usually a sign of improper water parameters whereas in both eyes could mean a bacterial infection.
If you think he has popeye you could add epsom salt (you can find it in a pharmacy) to his water as well. It is also usually 1tsp to a gallon but I've never used it with AQ salt so I don't know how much to add in addition.. Adding tannins in the water is good too. Epsom salt can be used long term till the swelling goes. You will have to do daily water changes with the treatment. :)