The acidity of powdered teas depends on the additives.
Powdered ice tea mix such as Lipton iced tea mix, for example, contains a lot of sugar in crystalline form. These are the shinny crystals one sees in the powder. This makes Lipton iced tea mix extremely acidic.
Cheaper quality Lipton iced tea mix that does not contain sugar crystals is alkaline and bitter tasting, and is healthier.
Indian and Sri Lankan black tea (red or yellow label) is pure powdered tea without any additives. It makes a very strong tea that is alkaline. It is a very healthy tea.