Rust colored speckles on Pebble Tec ..what is this?

[Andiejj]

I just noticed that we have rust colored speckles pn pebble tec. Most of it is on steps and shallow end. None in deep end except on the bench seat. I scrubbed an area really hard and it did not seem to make a difference. There are some areas that I have scraped my fingernail on and it came off. Any clue what this might be? My pool is crystal clear.

FC - 4
CC - 0
TC - 4
ph - 7.2
T/A - 50 **** currently adding baking soda to bring up
CH - 290
CYA - unknown

Here are some pics:

 

[PSW]

To find out if it is a metal (copper) stain, try rubbing a vitamin c tablet on an area for 2-3 minutes. If the stain lightens, then you are looking at a metal stain. If it does not lighten, it is likely organic. If it's organic, chlorine and or an enzyme should do the trick.