I too have lost some sps in the last couple of months, including: acro mille, acro gemmifera, a couple other acros, 3-4 acro frags, a chalice, and a couple of branching and plating montipora. while a few other sps's do fine: abrotanoides, porites, carolina, pocillopora. my thoughts are that your tank is new and needs time to "brake in". hobby tests kits are useless in this case: example, keeping po4 above .04, when the error is +/- .04. IMO finding a "smoking gun" is rare and the problem is most likely several factors. in my case i believe it was several factors. i found some montipora eating nudibranches, my no3 spiked to 5 ppm, tank was too new, my leds were running too bright. i also think some sps's will not thrive with leds and we must find the "right" sps's for led lit tanks.