yup.... if ya got a marine store around, stop in and pick up a qrt of on/off acid... it's better than the muriatic you get in the hardware store...
bit of advice... one, don't breathe the fumes, it will kick your a$$... two, when you put muriatic on concrete, if it's dry, it will be aggressive as he!!...
in other words, when i need to just do a mild clean, i'll prewet the floor... but in this case, i would just pour a few capfuls on the affected area dry, scrub it with a toothbrush, staying on the stain, than rinse....
if you just pour it out and scrub a larger area, it'll clean that area, and clean the he!! out of the surrounding area, kinda defeating the purpose..