Help...anyone know what this is?

[areceeg2]

My pool is 8 months old. It's a gunite pool using chlorine with a mineral filter. Over the winter a brownish has developed on all the vertical surfaces. The bottom and steps are fine. I've scrubbed them with a nylon brush but it does not come off. I've shocked the crap out of it and it does not bleach it out. The chemical levels of the water are perfect, according to a local pool supply company. I'll try to post a pic. Any advice would be appreciated. It ages the appearance of the pool.

[Phil.c]

Try a vitamin C tablet against the stain for a few hours, if the stain comes off then it's probably iron in your pool.

[areceeg2]

i would post a pi, but i don't know how. Does anyone know how?

[Denniswiseman]

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After testing as Phil.c suggests. Do a Ascorbic Acid Treatment