I need help with returning rust stains - picture included

I am truly at a loss. I cleaned many feet of sidewalk which has high iron in their well water. I thought I did a good job but nearly all the areas of concrete and vinyl I cleaned have some rust stains returning in 3 days.

I know the water I am using to clean has high iron and my only theory is that the iron is so high that as I flood the area with my surface cleaner, rinse with “fresh water”, apply my rust treatment (about 10-13oz of Ox acid per gallon) and rinse again that I am leaving behind enough iron particles to have the stains return.

Has anyone seen this before? What am I doing wrong?

I’d use F9 Barc and be done with it……I’ve never had a rust spot that couldn’t be removed with that stuff.

Any chance the irrigation system has just that much iron in it that it’s literally dumping rust onto the pavement when it runs? I don’t see any hardcore rust stains on the building or HVAC heat pumps so perhaps that’s not a possibility, but I’m just spitballing…

Also, I see in the “after three days” photo fresh stripes in the lawn. Perhaps the landscaper put out iron in liquid form? I know that in pellet form it’ll leave little rust-looking stains on a driveway/walkway if not swept/blown off after treatment. Once again, grasping here. Hopefully someone who’s had this happen before can get you a better answer. But, the initial before and after photos look awesome!

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Great suggestions, thanks.

A bit more info. We thought the rust stains were attributed to the sprinkler overspray. The property did shut off the sprinklers for the season before I started.

I also did another property just 3 weeks ago using basically the same method to remove rust on sidewalks and siding I will drive through there tomorrow to see how it looks. If it’s fine and the rust hasn’t returned like it did here it can rule out my process and the ox acid.

Side note: I have gone through about 150 gallons of rust remover. I purchased 5 gallon buckets ($125) of ox acid from Amazon and each bucket makes about 60 gallons.

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