blue stain on walls inground pool

[Shidal]

I have emptied my 10,000 gallon pool and the walls have blue staining on them. We have acid washed and brushed the inside and the blue stains along with other stains that were there when we moved in are still there. When we moved here the pool had water and hot mud creating dirty marks on the bottom, the pool was sanded at that time, and the dirty marks remained. However, there was not blue until this time. Is it caused from an elemental copper we put in to stop the black algae? Any advice would be very helpful. Thank you

[Guest]

A blue green stain on plaster is a copper stain. It could be from the algeacide. Another cause is low pH in the pool reacting with copper in the system (the heater coils for one place).

If you use trichlor tablets that can also be the cause due to its low pH.