Harpic, Cillit Bang or Toilet duck. (i tend to remove the labels, so the customer doesn't know what it is)
May sound a little crazy to use household cleaners, but they are all powerful limescale removers. I have tried different methods for years and always come back to using any of the above, by mopping the conservatory roof then hosing it down.
You can then either squeegie it off or with pure water depending on whether you are trad or wfp.