Eek, what a horror story! I'm kinda new here, too. These folks helped me rescue my pool that looked a lot worse than yours. Picture pea green soup, and you'll be close. Fortunately, I didn't have a clueless contractor to pick up after -- just a pool service that had been abusing our pool for the past several years. In order to get my pool back on track, I started by draining about half the water because my pools CYA was WAY too high, and the only way to get that number down is either to drain the pool or to practice some sort of water exchange. I elected to bite the bullet and I drained about half the contents of the pool. From that point forward, I SLAMmed the pool, and tested using the TF-100 kit. In less than a week, the results were dramatic. In about 10 days, I was able to finish SLAMming and had a crystal clear pool -- clearer than it had looked in a long time.
So what I'm getting at is just pay attention to what the old salts here tell you and you'll be able to get your pool back in shape. Also, if you do the maintenance yourself, instead of hiring a pool service, you'll save a ton of money and your pool will be healthier for it. Cuz, in my opinion, your average pool service shouldn't be allowed within a hundred yards of a pool. They're clueless about the problems they're creating that can't easily be solved. And in the process, things get steadily worse. I fired my pool service two months ago, and it's one of the smarter things I've done in recent months. And don't listen to the advice given out by the pool supply stores either. They're there to sell you chemicals, most of which you don't need. Really, all you the chems you need are chlorinating liquid (aka bleach, for algae control) and muriatic acid (to regulate pH). Well, if your CYAs get low, you can get some stabilizer, but you'll use it sparingly.
One comment I can make about draining a gunite pool. A few years ago, shortly after we bought this house, our "pool guy" let the algae get out of hand and couldn't correct the problem. So we elected to drain the pool and start over. What did I know? I didn't know about TFP back then. So we drained our 20k gallon pool dry, and had the pool guys even scrub down the sides and floor while it was empty. Then we refilled it. We had no problems with cracks at all. This was done during the summer too. It gets plenty hot down here in Houston, but we managed to dodge the bullet that sez you shouldn't drain a pool in hot weather. We were clueless then, but we got away with it.