Beach is what all professional pressure washing contractors use. At least the ones that know what they’re doing.
Think about it like this. You injecting a detergent or chemical into a stream of water so of course it’s going to be diluted.
For bleach you want about 1% hitting your siding. Just try and pull straight bleach if you get the 6% stuff from the store. If it turns the green or black algae brown in about 5 minutes you’re good to go. If it turns it brown in under a minute pre dilute it a little. If straight 6% doesn’t kill the algae go to a pool store and get 12.5% liquid shock. It’s no different than the bleach you buy in stores just stronger. I would get some Elemonator or other surfactant to add to your solution. Some people even use Gain laundry detergent. If you’re just a homeowner washing your own house that would probably be fine.
Be sure to rinse plants, landscaping, wood decks, and windows before applying solution. Let solution dwell for 5-10 minutes on house, don’t let it dry on the house so keep misting if need be, rinse with low pressure, and then rinse all plants and landscaping.