In my house, we make it in a large plastic...Um, what are they called...You generally make lemonaid in them and pour it into a glass. Oh I'm hopeless. But we generally fill that with a mix of hot and cool water, have 3 tea bags (same tea bags we use for our black tea) and a cup or so of sugar? Leave it out to seap, mix the sugar in, Put it in the frig over night and then the next day add Ice. That or we brew the tea in the teapot really strongly, pour that into the container, add cool water after putting in the sugar. (Slightly mixes the sugar as well as weakens the tea, filling the container up) Put it into the frig and then Ice the next day.
Do you mix the tea in before putting it into the frig? Or maybe you're not putting enough sugar?