Mine was done four weeks ago by Clontarf Marina and l got it back clean, no problems there. It cost me, though.
If l got to wash the deck l use Palmolive Original or the stuff on the photo. The Palmolive is brilliant to wash dishes with salt water too!
The KoalaKare (Supercheapauto) stuff l wash my bikes and boat deck with, and it works well, whoever never had real heavy dirt on my deck. A bit of scrubbing with a brush elbow grease added helps too.
We got enough pollution in Sydney as it is. My deck sometimes is black from the crap in the air. The Palmolive l use on the hull with success to remove the traces of the Mulligan's stew the boat is floating in.