Blue Stains on Plaster Surface

[Kit]

Having drained our in-ground gunite, saltwater spa for a pressure test, I noticed that the white plaster has faded bluish stains on all the surfaces. What might be the cause? Can it be easily removed now that the spa is empty? BTW, the spa is about 6 months old.

Thank you.

 

[YippeeSkippy]

Do you add any copper containing algaecides or have a mineral system for sanitation?

 

[Kit]

Do you add any copper containing algaecides or have a mineral system for sanitation?

No. I might add that the chemistry has always been in balance. However, I am experiencing a possible salt level issue & might have been guilty of adding too much additional salt. Might that be a factor? Thank you.

 

[pooldv]

The two most likely causes are calcium scaling or copper stains. Is the surface of the stain raised and rough? Do you have some test results? Both can be removed with dry acid in a sock or spraying muriatic acid on it and brushing.

Common sources of copper are
Mineral systems
Ionizers
Other "natural" sanitizers
Pucks or shock labeled "blue"
Algaecides
Eroded copper heater from pH below 7.0

More about scale here, Pool School - Calcium Scaling

 

[Kit]

The two most likely causes are calcium scaling or copper stains. Is the surface of the stain raised and rough? Do you have some test results? Both can be removed with dry acid in a sock or spraying muriatic acid on it and brushing.

Common sources of copper are
Mineral systems
Ionizers
Other "natural" sanitizers
Pucks or shock labeled "blue"
Algaecides
Eroded copper heater from pH below 7.0

More about scale here, Pool School - Calcium Scaling

No, this is not what I would consider as scaling. The surface is neither raised nor rough. It is not along the waterline on the tile. It is only on the white plaster surface. The plaster is smooth. There is just a spotty, bluish tinge in the plaster. I assume that it is not copper staining since none of the sources you listed would apply to my spa. BTW, I used a nylon brush with a 3:1 ratio of water/acid to see if I could remove the blue. No luck.

I would like to identify the cause so I can (1) remove the spotty blue discoloration if possible & (2) avoid the problem in the future. Some typical test results are as follows:

FC = 5
pH = 7.8 (target = 7.6)
CH = 350
TA = 90 (target = 80)
CYA = 60 (target = 70 - 80)
CC = 0.0

Thank you for your help.

 

[Kit]

I am thinking that this blueish tinge might simply be a reaction to the various pool chemicals. Does this make sense?