Wet & Forget vs D/2 for Outdoor Slate Patio?
Did a search and found some old posts, but not many comparing Wet & Forget with D/2, Simple Green Oxy Solve, and others.
I know about MSDSes and things like that, but looking up chemical names doesn't help me out much because concentration, method of application, and surfaces all affect how they work.
Seen a massive advertising blitz for Wet & Forget, but read that after just even a year or two it deposits salts and is very corrosive and damages the integrity of surfaces like stone. D/2 is considered "safe enough" to be used on gravestones and does not destroy them over time, apparently.
Anyway, the property I'm working on has a large slate patio that backs up to a bunch of woods. It looks very nice, except the slate hasn't been taken care of in what looks like a decade. It's covered in green lichen and mold and other growth. My first instinct is to pressure wash, but I'm worried about chipping the tiles (this is my first time cleaning a patio).
Some people swear by bleach (sodium hydroxide) mixed with water and a pump sprayer, but that can apparently stain the slate? The slate is dark grey apparently (looks rather black now). Also, Wet & Forget apparently takes many months to work. I don't mind scrubbing with hands or a brush on a pole if I can get it clean within a day. There are plants nearby and the house is on a well water, so I also don't want to use something too caustic or damaging to the environment.
The other thing I don't understand is that if D/2 is such a panacea, why can I only get it from a supply house and not at Home Depot or something like that?
Are there any other chemicals I should be looking into? Simple Green Oxy Solve makes some products... I've used their metal cleaner before and it worked fine, but idk. Also, there are three of these Simple Green pressure washer concentrates, (Total Outdoor, House and Siding, Concrete and Driveway) none of them say slate. I'm assuming total is the most gentle one, concrete is the strongest, house and siding in the middle?
This is all so confusing. I'll go on a website like Home Depot or YouTube or here on Reddit and see a bunch of boosted/sales reviews extolling how amazing Wet & Forget is, but they're all paid promotions. Then a bunch of 1-star reviews talking about it damaging materials, and taking months to work (I don't mind waiting 2 days or something but waiting 2 months to see the patio clean up is insane, I'd rather scrub the entire thing with a toothbrush lol).
Thank you in advance for your replies, and is there some other subreddit to which I should crosspost? This is all so confusing to me. I'm not worried about having to go to a supply house to buy things, and I don't mind if one product is more expensive than another, as long as it's not like $500 or something lol.