bluish dark green stain on gout line above water level

[neuro0]

Hi all,

Need the expert help here. This is a SWG pool. It is seen above water line and appearing in more area slowly. Tried rub it with the trichlor puck for about a minute but no help.
The pool was built last year. Tested the water with metal but none found. Will try Vitamin c tablet as soon as I find any. Pool was always clear.
pH 7.8
TA 70
CH 325
CYA 25-- adding more now
FC 3
CC 0

Thank you for any suggestion, advices!
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[attachment=0:2xqq84bu]20130416_170813_resized.jpg[/attachment:2xqq84bu]

 

[duraleigh]

Usually efflorescence is white but that's what it might be where minerals migrate to the surface from underneath the grout and tile. Try a 3:1 dilution of muriatic acid and water. If it foams, that will clean it.

 

[neuro0]

Thanks for the suggestion. Will try that when the rain stops.

 

[neuro0]

I just tried the aicd method. It starts to foam and the stain turn back. Does not look like it will come off even after scrubing it. Will the stain ID kit help me? Thanks!

 

[Bama Rambler]

If the stain turns black when you put acid on it, that sounds like copper staining. You can try rubbing a vitamin C tablet on it and see what that does.

 

[neuro0]

Finally got the chance to rub some vitamin c tab on it, it kinda of lighten it little but it could be just the vitamin c powder residual on them. What should I expect to see if this is copper stain? Will the vitamin c remove all the stain if this is copper. Thanks for all the help I can get.