You are all so very helpful. Update: My husband drained down the spa and squired a solution of meriatic acid (10%) and water. Boom. Stain completely gone. A neighbor was able to gingerly rub at a dark smear on the side of the pool and he actually was able to remove the stain. This was using a stainless brush which I am not a fan of and have not used. So, this being said, my local pool store suggested we brush the pool (used nylon brush) and put in a solution called Supercide (algea destroyer and stain remover). Honestly, I don't see much difference. Algea may look a little lighter in some areas. Sometimes your eyes play tricks.

Here's the readout. 14000 gallon pool. temp 85 degrees, algecide level 0, Protector 28 N, total solids 1700, saturation index -0.4, free chlorine 8.0, total chlorine 8.0, alkalinity 45, calcium hardness 220, ph 7.4, stabilizer 100. They suggested low alkalinity and had me buy equalizer. Then, muriatic acid. This was tested on Friday of last week. it is now Monday. I will probably get it tested again tonight as I will be near the pool store.