I gave you some thoughts on acid washing back in post #17. When my pool was acid washed, the sections that weren't completely destroyed, felt almost sticky. My hand didn't glide over it as before. Definitely etched. Definitely not as smooth as the pre-washed plaster finish. Granted, I've only had direct experience with the one acid wash that occurred in my own pool, but I just don't see how a contractor that is hired to apply plaster, who later has to acid wash it to correct the symptoms of a bungled installation and/or fill, can claim that to be an equitable solution.
And note that I said symptoms. Even if your contractor possesses the skill to acid wash your plaster finish to your aesthetic satisfaction (look and feel), I don't believe acid washing is going to cure the underlying cause of the symptoms, which in all likelihood was sub-standard application techniques. (And Matt has already given you the proof that establishes the fill was done incorrectly.)
Sorry, I didn't choose my consultant, the contractor did, so I don't know how to do that. I'm not sure I'd allow that again, knowing what I now know, but it happened to work out in my favor.
Here are some tips that someone taught me, that helped me get through the "negotiating" phase of my ordeal. Say as little as possible. Don't offer any information if you can help it. Don't admit to anything. And only ask questions, don't make claims or accusations. Let the other party hang itself. The fill information Matt gave you is a perfect example. Don't say something like: "I learned that my fill water was very aggressive. It's your fault that those stains were caused by the hose because you never tested the fill water beforehand!" That would allow him to make up some excuse, or blame you because you didn't test it, or claim that he did test it and buffered the water correctly, etc. Don't teach him how to defend his actions. You can lose all your leverage on that point. Instead, you ask: "Did you test the fill water before you put it in the pool?" and "Did you treat the fill water in any way before you put it in the pool" When he replies "No, why?" bingo! You've got him dead to rights. You don't even have to answer his question. Keep your cards to yourself. At most you say "Just wondering." Instead of giving him a way out of that blunder, you've captured a very important piece of evidence in your favor, just by asking questions. This is what I describing before, and why I was recommending exchanges in writing, and/or to have a witness present. If you can get him to answer a question like that in a certified letter, he's done. Or if he answers it in front of a third party. If that exchange happens only between you and he, verbally, and he later figures out why you asked him that, then he could come up with a lie or later claim he never said that. So prepare for your meeting. Figure out what you want to get him to say, admit. And prepare questions that would get him to say it.
This is how I got my contractor to incriminate himself, in writing. With that in hand, I had no trouble showing the CA Board that the damage was clearly the contractors doing, and that led to my positive resolution. Had I gone to court, I'd have presented the letters (or a witness) to the judge for the same results.
By the way, you should capture somehow the results of your fill water testing. Something that clearly establishes the current fill water chemistry and the date of the test. My fill water changes a bit throughout the year, because my municipality acquires it from multiple sources: a dam for part of the year, ground water wells other parts of the year. My fill water chemistry varies by season. You don't want some primary evidence disappearing on you. You might take your fill water to a pool store. If they get the same results, that'd suffice. Leslies, for example, gives you a dated printout. That might come in real handy if you have to take your evidence to the Board or a judge.
