Over the many years I have been keeping reef tanks I have learned that it is critically important to have stable, rock solid parameters, especially alkalinity. Like other reefers, I had no other choice but to use a hobby grade test kit to measure alkalinity. I tested weekly using a Salifert test kit and every now and then I would see a decent swing in results from one week to another.
Was it due to my calcium reactor not working properly, kalk in the kalk reactor expiring, a bad test kit, or was there another reason? The bottom line during those instances was that something happened in between my weekly tests to cause alkalinity to swing. And sometimes those swings impacted the health of my SPS.