Acid washing will reduce the life of your finish. It doesn't magically attack and remove calcium and leave plaster alone. It strips off the plaster and takes the calcium with it. It will not likely remove all the calcium. So what you're left with is some amount less calcium, but not a particularly more attractive finish (to my eye). And, as I said, a surface that will not last as long as it would have. That is best case. Unless you have a very light layer of calcium and a very skilled acid-washer-guy that really knows what he is doing, then you might get better looking results (but still lose plaster life).
Worst case, you'll destroy your finish and need to have it replaced.
This is based on my experience alone, in one plaster pool. YMMV.
Keep in mind: it is plaster that is holding all the little pebbles in place. Most pebble finishes, if not all, when first installed, are subjected to an acid wash. The purpose of that initial acid wash is to eat away just the right amount of plaster to reveal just the right amount of pebbles. When you subject the surface to another acid wash, which won't to much of anything to the little pebbles, what do you expect will happen to the plaster that was already at the perfect level relative to the pebbles?
Had I to do it over again, I would have left the pool surface alone, and bead-blasted the tile. I would then leave my glasses in the house and convince myself that the calcium streaks along the bottom were a tribute to the milky way, my own custom design, and left it at that. I would have enjoyed the pool, as is, until the plaster was shot, then replaced it.
At the very least, give PebbleTec support a call and see what they say about acid washing their product. They would know better than anyone, certainly better than me...
