I found this site as I was looking for an answer to my pool issue. I also have blue streaking, staining in my 3 year old gunite pool. From everything I have read, only copper causes blue staining. My water is professionally tested monthly and I have 2 years of records that show the water chemistry has been kept in balance. However, the hardness is very high as well as the conditioner. The water tests negative for copper and I do not have a heater. Several pool companies have been out to inspect but are also at a loss to explain the blue streaking/staining. The discoloration is on the walls as well as the floor of the pool. It is not sticky like algae, the pool water is crystal clear. However, if I scrape it hard with a screwdriver, it does come off, leaving white plaster behind it. It also seems to be accelerating in staining. A few other issues with the plaster.....I have a growing rebar stain, the surface is very rough and there is grey mottling everywhere. The 3 year old plaster looks like 10 year old plaster. It appears to be a major botch job from the plaster company, however I still cannot explain the blue staining. Help!!! Thanks for your time!