My post on a reddit thread from a year or so ago:

Ok, I have just been through this - a 35sqm deck that gets leaves and has grip tread up and goes black :( and a 90sqm second story deck that gets rain and sun and ages incredibly fast.

The first time you do this it's a big job, took me nearly a day of cleaning and two days of oiling (2 coats for most and 3 in a few areas). If you do it every year it's 2 - 1/2 days/ 1/2 a day of cleaning and the next day 1/2 a day of oiling.

My goto method now is:

Sodium percarbonate (buy from trademe) scrubbed on with a stiff brush. This loosens the dirt, kills mould and bleaches the fibres. https://www.trademe.co.nz/a/marketplace/business-farming-industry/farming-forestry/fertilising-pest-control/chemicals-treatments/listing/4393896187

Water blast with a patio cleaner (one of those with a spinny thing inside a brush head). This will clean off the dirt ideally without destroying the wood fibres and is much wider so takes a lot less time. https://www.bunnings.co.nz/gerni-classic-patio-cleaner_p0235530

Solvent (not water based) oil with the cheapest decking oil you can find - currently british paints at bunnings. The solvent based oils soak in, and water based ones leave a coating on top. This means if you miss a year no big deal, it won't flake it will just fade a bit more.

Honestly - if you are going to do it every year, buy the stupidly overpriced gear, the cabots oiling broom and pads are magic and so easy to use. A good sturdy stiff broom is worth its weight in gold for scrubbing, i broke 3 cheap ones before spending properly.

Edit: I see below some one said they have two people, one with a garden sprayer and one following with a speedbrush (similar to the cabots pads I imagine). This seems like an excellent idea and I'm jealous I never thought of it If I hadn't just done this years would 100% give it a go. Only issue i'd imagine is harsh solvents could ruin it so maybe a dedicated cheap sprayer? u/cthulthure what do you recommend?

and the whole thread: I have a large deck : r/newzealand