I sprayed moss killer to prevent moss from growing between the cracks of my paver stone driveway. I tested a small area first to make sure it wouldn't stain the paver stones. It looked fine after about a day–no stains–so I proceeded to spray the whole driveway.
It came out fine, except that, shockingly, one portion of the driveway became stained with a rust-like color. I tried power washing it out with water only, which worked a little bit, but it's still discolored.
What cleanser can I use to clean up the stain without damaging the stone? The stones look like this: