Every time I make iced black tea, it gets cloudy once it is cold. If I pour a glass and take long enough to drink it that it gets back to room temperature, it stops being cloudy. This doesn't happen when I make iced green tea or iced white tea, or even with a light bodied black tea like spring Darjeeling. I've heard that this can be caused by hard water, but I use a good water filter. I've also heard that adding citrus or vitamin c will keep it from clouding, but I don't like adding things to my tea. The flavor is not at all affected by the cloudiness, but it is too gross looking to serve to a guest or anything.
Why is this happening? And is there a way I can make it stop?