I have the same lights, and got the same results.
After my last purchase in January I put the Acros in a rack on the bottom. After talking to many guys, there were 2 reasons or even 3 why this happened. Your lights need to be at 40% on whites, but leaving them on the bottom for a month or 2 seemed to help. Then, feeding. Target feeding with Reef Roids or Reef Chilli, early and or evening, or both, before whites were on. #3, wasn't a answer I liked, and didn't expect, corals die. And I just lost one that went white over night after receiving. Just like a fish, corals die. Guys I've met, have incredible DT's, but this happens to them as well, their answer, welcome to the hobby. It doesn't sit well with me either, especially when others do so well. Very perplexing! These guys sell hundreds of frags, and keeping Acros is hard. Whole, large colonies turned white on them, very large colonies. I couldn't believe it! It would devastate me! But these guys always cut frags off, and as much as it hurts them, a frag is growing. Most vendors will tell you to cut the coral to save it, cutting a good portion above the bleaching.
My last recent buy from these guys, just 2-3 weeks ago, and about 18 frags, I lost one overnight.
Another coral recently, purchased in January, started bleaching at the middle, this I believe was due to a power head too close.
Also, on the days I visited these guys and asked many questions on Acros, both told me to make small changes, keep it simple, and remember: corals die, but if there's one part of the coral that is alive , your coral has a chance to recover and grow, but not the bleached part. All of this they proved, as they proceeded to remove 3-6 corals that were beyond repair, totally bleached white, and tossed to the round file.
Of course, this is my opinion, my observations, and my thoughts as I learn to keep Acros. Sorry for the long write, but I trust these guys, and this is their views as well. FWIW, many of the corals I've purchased from both Live and grow, and some, most, are fine. My advice is to search out a local reefer, from here or another forum, but remember, these guys don't bother to answer forums. If you buy from them, get to know them, the info comes out. I've never gotten half the info from any vendor, but your local reefer wants repeat business, and they are much cheaper, very much cheaper. Search, find, buy, and ask, ask, and ask again. Don't be so hard on yourself, I was and did second guess myself, even though most of my corals are fine, just part of a learning curve. Hope this explains a few of your questions, and future ones. Oh, high Nitrates, wasn't a cure or death factor, but dramatic changes surely was.
