The pinch of baking soda is helpful to keep the tea from turning cloudy. But it is optional. You don't have to add it. The basic recipe for Southern ice tea is this:
Brew it strong. The boiled tea should be black, just like coffee. Add the sugar after you have boiled it and steeped it and removed the bags while it is still warm. The warm tea helps the sugar to dissolve. Be generous with the sugar, but sweeten it to your taste. Most Southerners I know like moderate to well sweetened iced tea. There is no right or wrong way to sweeten. It is very individual. After sweetening the warm tea, you may add a pinch of baking soda to keep it from becoming cloudy. Then let cool to room temperature. Pour into a glass container with a lid and refrigerate. It simply tastes better when stored in a glass container than in a plastic container or old milk jug. Don't worry about it being too strong and dark. When you pour a glass, fill the glass up with lots of ice cubes (crushed ice is the best) and pour the tea over it. As the ice melts it will dilute the tea. Serve with slices of fresh lemon.
Note well: Only Yankees and other barbarians use "instant" iced tea. If you serve instant tea to your guests in the South, all your guests will know that your Momma did not raise you with any class or dignity.