You are not going to get rusty water from aluminum or manganese anode rods.
I don't know if you mentioned it but the glass lining in the tank is probably broken and the mild steel is rusting. That's if you don't have any galvanized nipples on the heater or fixtures where you see the rusty colored water.
IRB is not tied to the amount of iron in the water although there has to be some iron.
How much iron and hardness is in your cold water?