Plaster staining and condition

[lovehate]

We renovated a 20 year old pool in the spring of 2008. The company is from a nearby city who also handled the start-up fase, but assigned a tech who had never done a start-up. On some of his "brushing days", there was so much plaster coming off, that he couldn't see enough to finish, so he just skipped that part. From the beginning, I noticed what appeared to be staining on the new plaster. The renovator said he didn't know what the cause was. As the stains increased, he said it must be due to metals. Later we had tried to remove a couple of stains created by a some of metal roofing discs (reroof done shortly after pool put in). Put some kind of recommended powder into a sock and laid it on the stain for awhile. That removed the stain, but then the next day, noticed it had also bleached a long streak (draw line water down to bottom drain?) and then eventual blue stain to much of the plaster surface! Last fall the pool company needed to make a crack (another long story), so they drained the pool down and did an acid wash. The plaster was already quite degraded (starting to look like pumice in places), and the pool guy said it was more evidence that we had really mishandled the water balance.Then it took 10 days for them to figure how best effect the repair, during which the pool sat empty. They finally secured the crack with using Torque-lock, backfilled to the surface with some kind of white cement, but didn't top coat the surface with plaster. By the afternoon of the completion day, the plaster was starting to craze, and the pool guy said they needed to get water in the pool fast. So now we have a very visible crack repair as the plaster appears to be staining at an even greater rate, but this "cement" is brilliant white. Tried to get them to coat with plaster (as this was their original plan), but they tell me "they've done all they can to help me". On the weekend while swimming, I investigated the underwater plaster condition. The crazing is still evident up close, the staining is increasing at an exponential rate, and there are little divots appearing in place. The pool company maintains that we have mishandled the water. I have tested it frequently, both at home at local pool company. At most the ph has been up to 7.7 or 7.8. Depending on the time of year, they've recommended either doing nothing or adding a quart of acid. I've had the water tested at the state university for metals, but levels barely register. We have fairly hard water here, but all other chemicals have been fine. Water appearance has always been great - never cloudy. We've never had a problem with algae, but it seems whenever I add acid there's a bigger problem with calcium scaling on the tile (or is this my imagination?). I'm concerned that we're headed for another plaster job in the near future. Advice PLEASE!