I’m big on OneRestore for a lot of stains, I’ll wet the surface, apply straight, wait 5 minutes or so, don’t let dry out, add a second application, don’t rinse in between applications, then rinse real good. I’ve also used Prosoco 600. Those little spots might be fertilizer staining? https://prosoco.com/Content/Documents/Product/SK_600_PDS_031318_C.pdf
Kinda looks like calcium carbonate buildup. But on the other hand sometimes when new concrete gets wet all the time it pulls the magnesium to the surface, and that cannot be removed. Cream layer looks delicate, I am thinking that will be altered if you attempt any type of acid cleaning.
Either one will be fine, but you need to do that whole little section, spray it on, lightly scrub, mainly to saturate. Then, like Kentucky said, I’d spray another light coat on that section and then surface clean the whole porch. You need to tell them, that section may look a little whiter than the others.
We just did it Monday. I rinsed off the looser stuff and sprayed One Restore straight on the obvious red stains. It foamed a lot, and I rinsed after about 3 minutes. Her watering the planters over a few years seemed to have ‘worn away’ the top bluish concrete layer and it was more of a medium grey once the brown oxides were taken out.
My worker took pics and I will post soon as he sends them.