Dark Greyish stain removal?


Bronze Supporter
Aug 7, 2019
Hi - this house was purchased about 2.5 yrs ago, and since then I have had two types of stains found on the pool - one green/yellow and likely from organic algae growth. I removed most of it by directly putting vitamin c on areas. The other are dark grey "stripes" which sometimes have some yelowish areas too.

The pool has been slammed a couple times with no reduction in dark gray stripes. pool water was tested and both iron and copper were found low. I dont use a copper-based algecide, but previous owner may have. I have not fully drained pool since purchase, but partially (1/2) drained it previously to reduce CYA.

Dark stripes are not black algae, not slimy or round, but do feel a bit rough. I tested with vitamin c by filling sock attached to heavy filled tupperware on a grey area - the stain turned slightly reddish in attached picture the center of the stain had vit c applied

I am currently testing another stain spot with dry acid in a different sock/tupperware.

? Why in straight lines could this be rebar related?
1) how to treat the remaining yellow stains which are on vertical walls w vit c?

2) Thoughts on dark line stains?fullsizeoutput_9e0.jpeg
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