1350-1450 is recommended, not sure what the minimum is for usability-One key thing is if your mag is depleted, msot likely the other two (alk and calc) are probably off a little, or you may be adding excess of those if the magnesium isn't there for the corals to utilize to grow. Keep an eye on all three and you'll be best off, but yea, 1200 is a bit low on mag; not enough to cause problems, but enough you won't have as ideal of growth and possibly color.