i used a 2700psi pressure washer with one of the circular power sprayer set ups you put on the end of the wand and move it around like a floor sander/buffer
works great and is real fast. I have the original composite decking made mostly out of wood fibers as well
this is the type of attachment i was talking about, there are many different makers out there
https://www.walmart.com/ip/Hyper-Tou...ntent=In-store