What are teses tiny rust-like stains?

[poolbee]

I have been finding tiny specks of brown/rust color on my steps(plastic), in the skimmer boxes and around the white aluminum coping. What might be causing these? They are only as big as a grain of sand to start, are raised a bit and are very difficult to remove. I have been scraping the worst ones off with my fingernail and they don't come off easily. Ive tried the Mr. Clean Magic Eraser and Softscrub with minimal success.
I have a vinyl liner pool, SWG with no mineral additive. CAL is 210 and my copper tested at <.1 at the pool store.
Would anyone know what it is and a good way to remove it?

[mbar]

When you get it off, rub it between your fingers, if it feels slimy it is algae, if it feels gritty, it's not. You can rub a crushed vitamin C tablet, or some ph down on it - if it disappears, then it is from metals.

[poolbee]

I just read a post by Waterbear about iron stains and salt. My builder used Morton table salt-550 lbs of it. Would that have any effect? The bags, as I recall, said 99.6% pure. Could that also cause what looks like rusting of screws in the water? My builder came by and replaced some screws but cleaned off some with pH down and left me the bag for future leaning.
It is not slimy, but gritty.
How do I get rid of the metals in the pool if that is the cause?

[mbar]

You can use ascorbic acid (vitaminC). Bring your ph down to 7.2, crush some vitamin C tablets and put them in a sock. Rub them on the stains, the stains should go away. If you have a lot of stains you may want to purchase some ascorbic acid. Add some sequeserant, such as jack's magic, or metal free, or sequasol something that says it will get metal out. Sometimes just adding some sequesterant along with bringing down your ph, the stains will go away.

[poolbee]

I tried cleaning the skimmer box and stairs with cal hypo and some pH down. Cal hypo really didn't do much of anything. pH down did a good job on some and OK on other stains, but really didn't do anything on the stairs.
I'll try some vit. C and see what happens. My pH was up,added muriatic acid and brought it down to 7.4 last night.
Thanks for the information!

[waterbear]

Table salt should NEVER be used in a pool. It contains an anti-caking agent (yellow prussiate of soda) which is a iron compound. Only use pool salt, solar salt, or water softener pellets that don't contain iron removers or water softener tank cleaners that are at least 99.5% pure salt!