With sps there can be millions of reasons for bleaching. With 175 mh your acros aren't going to bleach and die. They may turn brown from lack of light but they would still have enough to live and probably grow very well. I think a couple of things in that tank could be affecting the coral. The leathers could be launching chem warfare against the sps (happens very often), Your light cycle could be too long resulting in too much light intake and bleaching occurs. If I were you I would get an easier more hardy sps like birdsnest or some monti plate and see how that does. I think your lights are plenty.