No, purple up will not cause cyano. Overfeeding is the main cause, along with low water current.
You do have to watch your calcium levels. Purple up will make it climb. I wouldn't worry too much about the iodine, water changes should keep things in check.
Purple up uses calcium to help build the coraline algae. If you have the right numbers for phosphates (0.2 and below) and calcium at 400/450 coraline will grow good and fast.