LOL, I would never do that on brown stained wood. You’re a brave man.
Just like a roof , let it sit for awhile. It will lighten up over next couple of weeks. The idea is to bleach it out. with a grey stained house may be a little lighter, but better than green and the mildew will be dead. Think a really bad deck that you went too strong on what it looks like in a week or two. That siding was no different than old grey deck with stains on that we’ve all done where the people just wanted to kill the slime.
Normally I wouldn’t either. Just happened to be the perfect situation to test it on. They’re just hoping to limp that roof along for another year or two and then replace it and when they do that I guess they’re going to address the cedar. There’s not much stain remaining anyhow and what is there is in horrible shape.
I don’t clean a whole lot of cedar decks and the ones I’ve done were either unfinished (no stain) or I was doing a complete stripping and cleaning and staining. So maybe my experience is not the best rule of thumb.
If you don’t over do the SH you can get rid of the algae and at least maintain a silver patina. A lot of times the wood will still have green showing but it will disappear after A FEW DAYS, leaving behind silver"ish" wood. Just don’t hit it with pressure, use the SH at about 15-20% SH to water per gal. It will not look the same as what is above it but it will get back to that look in a few months if you don’t go too hot. If you go too hot you will know because the wood will be whitened. Basically you will need to experiment with your mix but don’t be inpatient.
