In some circles of the pool industry, it is believed that calcium “naturally” releases from a new swimming plaster surface while it cures, (or more accurately, hydrates), and thereby continuing to increase the calcium hardness (CH) of the pool water during the first several months. This is a false belief.
However, if the tap water used to fill the freshly plastered pool is aggressive, then yes, calcium will be dissolved from the plaster surface, thereby increasing the CH level of the pool water during that process. The pH also rises in this situation. In fact, even balanced (zero CSI) tap water will usually dissolve a small amount of calcium when it first comes into contact with a new plaster surface.
Furthermore, when the TA of the tap water is low, the higher the pH will become after filling. The best way to combat the pH rising above 8.5 as the pool fills, is to raise the alkalinity content of the fill water before it even goes into the pool. Adding sodium bicarbonate to the tap water (to raise the TA above 200 ppm) before it is used to fill the pool is the best way to prevent the pH from soaring so high. This also helps prevent calcium from being dissolved from the plaster surface.
During the first month, a plaster surface becomes sufficiently hydrated and carbonated, which means it becomes less soluble. After one month, if the water is in balance (zero CSI), it is unlikely that any additional calcium will be dissolved from the plaster surface. If the plaster quality is good, there is no “natural” tendency for calcium to be released from pool plaster. Calcium levels do not automatically rise, and therefore, low levels of CH should be corrected immediately.
A good general recommendation for new plaster pools is to raise the calcium level to a minimum of 200 ppm, the TA to a minimum of 120, and to ensure that the CSI is a slightly positive number as soon as possible and during the first month. The main point being, new pool plaster requires a positive CSI (for one month) to protect it and to prevent a loss of calcium from the surface. If that is followed, then very little calcium will be dissolved from the surface, ensuring a smooth, dense, durable, and long-lasting plaster surface.
However, this is contingent on the plaster quality being good. If there is any continued and significant increase in the calcium level after one month has past (accounting for evaporation or Cal Hypo additions, etc.), it is possible that the workmanship of the plaster was sub-standard.
See this post: aggressive-water-versus-improper-pool-plastering-t51900.html
See also this post: ten-guidelines-for-quality-pool-plaster-t42957.html