Instant Ocean causing KH spike??

[Myka]

140 mg/l = 140 ppm = 7.84 dKH = 2.8 meq/l

This reading is not out of the normal range. I actually prefer my alk to be significantly higher at 9-10 dKH (160-178 ppm). Alkalinity is definately not your culprit. In my experience IO has varied very little from one bucket to another...sticking right around 11 dKH. I have had the alkalinity go up to 17 or 18 dKH in my tank, and the corals were just starting to show stress, but I didn't lose any.

If I were you I would be carefully doing a 50-75% water change as soon as I found out about the crash, and then proceed to do daily water changes of 30-50% until everything straightened out. Carefully, as in being sure to match temp and salinity very closely, and watching the critters for increased irritation.