I think its a big swing in my tanks, but in yours I'm not sure.
You are in essence losing one degree of alkalinity in a 24 hour period, every single day. If you think about it, your alk is never stable, its constantly in flux. If you had an entire tank of euphylia I don't think it would mind. Even montiporas can tolerate tank perimters swings......but if you are trying to keep the "harder" SPS, and are having a hard time with growth and color, I'd buy a couple of dosing pumps from BRS and two digital timers, and call it good.