Don't know how restaurants do it but I make pretty darn good tea by using Lipton's orange pekoe and pekoe blend. I make it by pouring about 40 oz of hot but not quite boiling water over 2 large tea bags, Cover and let steep for several minutes. I dilute with more water until I get that "just right" beautiful tea color.
The water is very important. City tap water with chlorine will change the taste. Check the ice in your freezer. If it is not sparkling clear, it has impurities. Try making your tea and ice with bottled water. The ice at the restaurant is always very nearly crystal clear.