Dingy plaster

[nbkg72t]

We are entering season 5 of our pool. The light blue plaster is looking 'dingy'. Don't notice it during the day but after the sun goes behind the trees and particularly when the pump stops for the day and the water is still, you can see it. It is not algae. Doesn't dust up upon brushing. In fact, even heavy brushing doesn't get rid of it. I assume it is some sort of mineral or other calcium build up. If I scatter some light acid powder (essentially a mini acid-wash) it restores the crisp look of the original plaster in that particular spot but (obviously) not evenly throughout the pool.

It is purely an aesthetic issue. Water is otherwise very clear and the chemistry remains fine (FC: 7, CC: 0, Ph 7.5, TA: 6, Cal: 475; CYA: 80). Calcium has always been unusually high in the pool so I try to keep the CSI consistently in the negative but no worse than -.6

What are my options? Would it be reasonable that we'd need a drain and acid wash at the end of season 5?

Thanks in advance

 

[Texas Splash]

Odd that you seem to be experience what seems like a calcium scale issue if the CSI is consistently negative. Will posting any pics help to show what you are seeing? We can get some plaster experts involved to try and assist.

 

[zea3]

Do you close the pool over winter? Sometimes over winter the pH will rise enough to start calcium scale formation. Try dropping the pH to 7.0 and see if that helps. It may take a couple of weeks of pH at 7.0 to see results.

 

[nbkg72t]

We leave the pool open over the winter. I've attached some pics. The issue doesn't translate as well through pictures but you can probably make out some of the splotchy 'dingy' parts.

 

[Texas Splash]

The pics are a bit difficult to see, but we'll tag @onBalance in case there's something he would like to add.

 

[ajw22]

Many blue pigments used in plaster soon bleach out, due to a continuous chlorine residual as is normal. If there was also a gray pigment added (along with the blue), making it a blue-gray color, then the blue color will disappear and leave the plaster a simple gray color.

Some use the good (non-bleaching) inorganic blue pigment in their plaster mix.

I suspect your blue color is bleaching out.

 

[onBalance]

While some blue colors may lose their color in time, I suspect this issue, at year five, and after a winter time, has more to do with minor scaling. Consider the suggestion that zea3 provided.