Unidentified Dark Areas Under Tile Line

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Good report. If his treatment works, I might be tempted to suggest you only pay 50% of the cost since you had nothing to do with the cause but he did.

PB may balk at that but it might be worth a shot.
 
Dave...thanks. I know this issue is controversial as to cause. His remarks were leaning toward a prior chemical imbalance. I took exception and said I am very careful about water balance. He asked what my settings were. When I got to CH at 300, he said that seemed high. Anyway we''ll see. I do appreciate the suggestion.
 
300 is close to perfect, if not perfect. It is not too high.

As I indicated earlier, I don't think anything like this has been reported on the forum over the years so a water balance issue really is highly unlikely.
 
Re: Unidentified Dark Areas Under Tile Line - Update 1/16/13

The no-drain acid wash began Monday 1/7 and continued until Tuesday 1/15 with pump running 7X24 for 5 days. The treatment did lighten the dark areas considerably. The spa was completely drained and acid washed and remained dry for 3 days. Industrial grade Sodium Bicarbonate added Friday 1/11 (approx. 40 lbs.) to restore ph/ta in pool. Approximately 1340 gallons drained from pool Tuesday 1/15 to view dark areas and torch remaining tough spots. Torch helped some but not much. The finish expert called today 1/16 advising to fill the pool that his "helper" should not have drained water. Apparently his "helper" didn't use enough acid during the treatment. They are returning Monday 1/21 to perform another no-drain acid treatment to run for 5 days. The finish expert advises that this will completely eliminate any remaining dark areas.

Today 1/16 I replenished the 1340 gallons. I checked and my PH is 7.7 with TA at 250 (Goal is 70). My CH is at 500. MY FC is at 6.0. I haven't tested CYA yet. So I ran the Pool Calculator with the intent of lowering PH to 7.0 to reduce the TA. The PC advised to add 3 quarts 1 cup of MA which has been done. I'll let the pool circulate and retest PH, TA, CH and CYA around noon on 1/17.

More to follow next week.
 
I am in agreement with Dave S.
The following is a list of contradictions by the "finish expert."
If the discoloration was due to improper water chemistry balance, then the entire plaster surface would be affected, not just below the tile.
"Hydration discoloration" is a cement problem, not a water chemistry problem. The plaster mix has a pH of about 12.0.
If 300 ppm of CH leads to discoloration, most pools in Arizona have a CH higher than 400 ppm. So wouldn't every pool discolor if that was the cause? But that doesn't happen.
If 300 ppm of CH leads to discoloration, your water now contains 500 ppm of CH. So is the plaster surface turning dark everywhere? Of course not.
The "finish expert" caused over 200 ppm of CH to be removed from the plaster surface. Ask him why that is good for the plaster surface? For your 11,600 gallon pool, 200 ppm is about 20 pounds of plaster material.
Ask him if aggressive water is bad for plaster. Yet his treatment made the water have a CSI of a (negative) -4.0.
Suggest to him that the surface is now ETCHED, and doesn't that age the pool 3 to 5 years? Why would you want that and pay for that?
An etched surface will stain and collect dirt easier and quicker. He is not doing you any favors. Especially if he charges you.
 
onBalance....appreciate your input. Your assessment left me with a queazy feeling. Since the finish expert was sub-contracted by our pool builder, who is rated as one of the top builders in our area, I felt confident that both the PB and finish expert knew what they were doing. Our finish has a 20 year warranty. Granted there is an issue as to who should pay, exact cause and how aggressive the treatments should be. For now we're simply trying to rectify the problem. I have a call in to our PB as of this writing to confirm the plan and impact on the finish.
 
I am sorry to be the bearer of bad news. I know my comments were blunt, but I think full disclosure is appropriate, and I am tired of pool owners getting a raw deal by some plaster people. The finish expert knows what he is doing, if you know what I mean. The PB, on the other hand, may not really understand the mechanics and long-term effects, even if he is a top builder and knows all about building a pool. And I am sure your warranty doesn't cover "improper water chemistry," which it isn't, but will be used as an excuse, and which the expert has already suggested.
 
See my post lowering-calcium-hardness-alkalinity-t55404.html regarding water balancing after acid wash.
Meanwhile, pool builder contacted plaster rep with batch number of product when pool was built(completed April 1, 2011) and for an on-site inspection of the pool. Still waiting...apparently the rep is booked two weeks in advance. Stains have almost disappeared especially with fill water above the stain line. Apparently we had staining on other areas of the wall and floor that I never noticed that were removed also. When water is lowered, you can still see a faint outline but only along the tile line. Have been cleaning filter almost every other day for a week. Brushing produces deposits in filter amounting to approximately 1 cup per brushing of what I call sand (the contractor calls quartz). Says this is "normal" since we had so much calcium deposited on plaster. Almost like when the pool was new with start up procedures. Changed out filters yesterday. Still having issues getting Alkalinity within 70 range per my above link to another post. What a "nerve-racking" experience!
 
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