IMHO,and i dont mean to sound negitive,ditch that fsc,why you may ask,with the flow rate you have on the unit get yourself a twin turbo nozzle,from what i see in the video it didnt remove the lichen(correct me if i'm wrong) which we all know is a sod to remove unless you use a pre treatment or heat ,you still had to go over it with a lance/nozzle setup.
Little tip invest in a water broom ideal for the final rinse down,sweeping with a brush is a waste of time and tbh you really get no where doing it as your just moving the crap around your'll see one day when you come up to a really bad mossy one theres also the hassle of wet sand to
At least you had from what i see was a quite a flat drive,with fsc problems occur when you have dips what happens is your'll create a pond under the fsc,unless you got real power the thing just ponds and the jets dont have a good effect
The video is good,but a bit more about the unit would have been nice,ie what it can do and what you can do with it.
Also might be an idea to do a part 2,go back on a really dry day and show how to do the re-sanding
summit thats not showen alot on youtube
All in all least you had the balls to do a video,which is more than i would(be to busy laughing all the time
)
Just my points of view and i dont mean in any way to offend
good luck