Any Idea What This Stain Might Be?

[vela]

I have kept all my numbers in range since initial fill back in January. Currently:

FC - 7.0
CC - 0.0
pH - 7.7
TA - 40
CH - 450
CYA - 40
Borates - 30

What's weird about it is that it appears as if my pool cleaner is cleaning the bottom part off (looks like tire marks at the base), but doesn't make it all the way up the wall. I did brush twice a week for the first month and once a week ever since. Has anyone seen this before?

 

[pooldv]

Does it feel rough?

Read through this, Diagnosing Pool Plaster Problems

 

[vela]

No there is no roughness to it. It all feels to be on the same plane. I've read that post over and over and I'd convince myself that it was from that first paragraph. It's just so odd that the pool cleaner seems to do something to it, but the brushing does not.

 

[onBalance]

It appears from the two pictures that the walls of the pool are darkened and grayish, while the bottom of the pool has remained white.
So I agree that the first paragraph of the article on Diagnosing Pool Plaster Problems best describes what causes this darkening of white pool plaster.
This is known as gray mottling discoloration, is smooth to the touch, and therefore, is not due to calcium scale.
It is very unlikely that the pool cleaner is doing anything to the plaster color.
I suggest a call to the contractor.

 

[vela]

Thanks onBalance. The walls all around appear darker than the bottom (especially in certain light). I'm just afraid that the contractor will want to do an acid wash or something else that will shorten the plaster life. I know plaster eventually needs replacing, but I didn't expect to see defects on year 1. I would certainly not want them to do anything until the season is over.