Rusty type stain on my steps-( pic inside)

[freddyttt]

Have this rusty type stain upon opening of pool. tried the magic spong which got 75% off but some remains-. any ideas?? on what it is and how to remove it??

thanks-


http://i3.photobucket.com/albums/y78/freddyttt/IMAG0318_zpsbxdlj6hl.jpg (http://s3.photobucket.com/user/freddyttt/media/IMAG0318_zpsbxdlj6hl.jpg.html)

[Watermom]

Could it be an iron stain? Do you fill from a well?

[freddyttt]

Thanks no I do not fill from a well. however iron was my thought. anyway to remove it...