what is causing this green stain in grout ?

[donconway]

hi can anyone give me some guidance about what is causing this greenish - blueish staining on the grout ,,,, this is a saltwater pool about a year old ,,,, the grout is most likely white cement ,,,, i believe all the basic chemistry is good ,,,, this is a customers pool of mine i have a small pool company in costa rica but i have never seen this happen before and looking for answers ,,,, it started about 2 months ago and is getting worse and it is appearing all over pool ,,, brusing with a steel brush didn't help and applying granular chlorine turned it black ,,,, any guidance would be much appreciated

 

[domct203]

Welcome to the forum.

Looks like possible copper staining. Have you or the customer used any copper based algaecide?

Do you have a way to check the water for metals content?

Dom

 

[donconway]

Welcome to the forum.

Looks like possible copper staining. Have you or the customer used any copper based algaecide?

Do you have a way to check the water for metals content?

Dom

no ,,,, but since this house is in the mountains and gets its water from a natural source ,,,, it may have some minerals ,,,, so i will get a test kit for copper ,,,,, thank you for that suggestion