Softwash on this textured render today - really course surface. Wet it up, then washed it initially with 4% SH using 40 degree fine fan jet nozzle to get as much mix into the little crevices as possible. Used quite a lot of mix. Then hit the ledge stains with a high concentrated mix. Didn’t rinse much due to texture and weather was perfect so it wasn’t drying out quickly, so I just repeated another few layers of 6% SH. Red algae flared and disappeared after a while, and most of the other algae staining is all but gone. The stains under window sill ledges seem immovable. I used a decently strong fresh mix of oxalic acid sprayed on with garden sprayer next on them but obv not rust as I didn’t notice any change after leavening to dwell and rinsing thoroughly. I lastly applied a neat hypo mix to them and left tonight hoping they work away over night. Personally given that they’ve hardly changed since I started the job. Any ideas on how to remove them ? I mean I thought of a specialist gel product that screw softwash manufacturers sell but given they’ve hardly changed at all I don’t hold out much hope. Maybe the water has etched the render or something weird ? Any pros got an idea on this one thanks ?