Low alkalinity levels in pool water can result in:

Low alkalinity levels in pool water primarily affect the pool's ability to stabilize pH levels. When total alkalinity is low, it can lead to fluctuations in pH, making it challenging to maintain a balanced and stable pH in the water. This instability can be harmful to both the pool water and its surfaces.

Additionally, low alkalinity can lead to corrosive conditions. As the pH becomes more acidic due to low alkalinity, it can cause damage not only to the pool surfaces, particularly plaster, but also to other equipment and fixtures. This emphasizes the importance of maintaining appropriate alkalinity levels to prevent damage over time.

The mention of scale formation in option A might relate more to high alkalinity or high pH conditions. However, with low alkalinity, the risk of corrosion becomes more pronounced, and plaster damage occurs as the acidic water attacks the surface. Therefore, the correct conclusion from the choices provided encompasses the harsh effects that low alkalinity can have, particularly concerning damage to pool surfaces, thus supporting the selection of the comprehensive answer that includes both pillar points regarding scale formation as well as damage to plaster surfaces.