I had my first frag melt on me too. The second frag I got is now doing well...didn't change anything in the tank, just how I treated them to get them acclimated. Who knows if this will help...but here's what I did:
Started them in the cave, completely protected from light and flow. They opened up and I waited a few days to start moving them into the light. When I did move them into the light, they would "mushroom"...for lack of a better description they basically turned their skirts down and looked like little mushrooms. The first frag I had did that and melted shortly after. Any time I saw that sign of stress I just put them back in the cave for a couple days. Probably not the BEST thing to keep moving them, but if they stayed in the light they'd melt and so I kept moving them into the cave for a few days, then back out into the light for longer and longer periods of time. First it was in the light for a day at a time, then 2, 3, etc...
It took about 2 weeks to acclimate them to the light like this. Eventually they stopped showing signs of light stress and were happily getting blasted by light in the front of my tank. I didn't get much growth out of them with them sitting in a little area protected from flow...but they are now sitting in an area that gets pretty constant direct flow and they seem extremely happy. The 3 polyp frag I picked up now has more than 10 polyps on it after just over a month in my tank.