OK, I kinda missed piecing that together. I'm gonna guess that your case might not be as open and shut as you think, and/or might not yield what you hope. It looks like your finish is now 17 years old, and has some pebbles coming loose. Theoretically, that could happen without an acid wash. How will you prove that it was the acid wash, and not age, or 17 years of poor water chemistry? I'm not saying it
was age or chemistry, I'm saying you might have to
prove it wasn't, because the defendant might make that claim (and legitimately could).
Did you keep water chemistry records? Can you prove what the pool guy did, or didn't do, during the acid wash? You can make
@JoyfulNoise's claim that a pool should never be acid washed (I happen to strongly agree with that!), but are you going to be able to educate a judge about pool plaster chemical make up? Even if you understood it yourself? Not in small claims, if that's where you end up, because you get about 5 minutes to make your case. If you try to go to Superior Court with this, only the lawyers will come away with any money. Because:
There is the matter of actual damages.
If you can prove the acid wash caused damage, what are
your damages? A few pebbles falling out of a 17-year-old pool? It would be pretty unfair to the pool guy if the judge awarded you a brand new finish, if that's what you're after. Something pro-rated would not be out of line, but even that would be somewhat far-fetched. And how are you (or the judge) to ascertain how long the finish would have lasted without being acid washed? What amount of pool use have you been denied? And the fact that you've been using it for six years is not going to help your case. What's the actual dollar figure you think that this could fetch you? I don't think all that much, if any. Probably not as much as the stress this is going to cost you. And certainly not more than a lawyer would take. (Though I doubt a lawyer would even take this case. Not an honest one, anyway.)
I'm just playing devil's advocate. You might have to adjust your expectations. My pool looked like a bomb was set off in it, the day of the acid wash. I had a hundred pictures showing my plaster in tatters and shreds, on the edge of being dangerous to use. I didn't have to prove much of anything, and my finish was only about four years old at that point, and the guys that destroyed it were the same guys that had been doing the pool chemistry maintenance since it was built, so they had no case about the age of the finish or condition of the water.