IME, low nutrients starved corals to the point they pale out, but I haven't lost any to them being low. That's just my experience with it and possibly luck. Too high of nutrients as we know, will brown them out (not the case here). If your nitrates are 8 and your phosphates are low but not zero, that seems to be a good level many strive for.
Correct me if I'm wrong, but one of the pics looks like there is cyano on the rocks right?
I agree that they look dead, you have to test your water, any stray voltage? I know you dip, but sometimes pest still get thru. You may have to check and check again.
Sometimes acros just die out of nowhere.