We downstream it, 50/50. w/dwell time 10-15m. So far that has worked for us. I can't really say how long before the oxidation comes back, would assume a year or so. I honestly talk folks out of getting the whole house done, it's a lot of money for something that's just going to come back. Once folks realise it's going to come back, they are happy to just get a standard wash. Had one house, we did normal softwash on three side and the f13 on one side. This side was messed up by a previous company. Took a $180 wash up to a $300 wash. Gotta be careful at the edges so you don't get overspray on the walls you don't want to treat with f13.
We downstream it, 50/50. After doing tests on our house, the 50/50 downstream worked best. Yes, correct, downstreaming adds more water to the mix.
I've known people to downstream directly from the jug of f13. My take is if DSing at 50/50 works, then straight is just over kill. The more f13 you use, the more you need to worry about plants. Even with our mix, we water, water, water, then water some more. Just to make sure it doesn't get sucked up the roots of the plants. and rinse the top of the plants.