Looks like rust to me. Or are you talking about real rust?!

I had a bag of dolomite I was using to weigh down a BB hoop get rained on and form a dark brown puddle. It filled a gallon jug about 1/4 and I added water because I didn't want to over do it. Nothing changed. I also use superthrive, fulvic acid, mycorrhizae, and Floralicious plus. My non-soil is 2/3 medium quality + 1/3 Ocean Forest with polymers, coco-peat, and perlite added(foxfarm). I switched to all ocean forest--as dirt--later (those 6 are under a foot so I don't know how much that will help, yet). Should I try so thrivealive or is that just overlap?

I'm new to soil--changing those DWCs every 2 weeks was making discretion difficult.