Hi there,
There exists a calcium solubility threshold level, and it is usually reported to be anywhere from 550-600 ppm. This means that if water in a tank has a Ca level of 400 ppm, you can add more Ca to the tank until the level reaches 600 ppm. If you add any more Ca after it reaches this threshold, it will not dissolve into the water.
It now appears probable that the "threshold" level can vary depending on conditions in the tank. One probable relationship is with pH and/or alkalinity. It appears that when the pH and/or alk is low, the Ca threshold level may be higher somewhere above 800 ppm. So one could add Ca in their tanks up to this level. Once Ca is up to this 800 ppm level, if the tank alkalinity and/or pH was increased for some reason and the threshold jumped back down to 550-600 ppm, a major snowstorm would happen. It woudd make your tank look like milk.
Hope this helps,
sam