I would say that it is bc of the lighting. Im not sure about the salt level, im sure its not too harmful for your salt level to be that low, are you using a refractometer or hydrometer. bc if your using a hydrometer your salt is prolly at .027.. usually the there off by abuot .005. Do you have any other sps under that lighting? I tried a monti cap under my old 130 watt in a 20 long tank, and it actually shrunk in size. Also I would raise the temp up to about 78 atleast. I like 80.
I keep my 315G at 75F. I don't think that it's too low for the corals but if the temp swings say 75-84 then you got issues. Mine is held stable by my chiller I set it to whatever I want and it holds it steady even with 1200 Watts of halides