For a pool with total alkalinity of 50 ppm, which chemical is most appropriate to increase this level?

Sodium bicarbonate is the most appropriate choice for increasing total alkalinity in a pool with a level of 50 ppm. Total alkalinity is a measure of the water's ability to resist changes in pH and acts as a buffer, helping to maintain stable pH levels. Sodium bicarbonate is specifically effective in raising total alkalinity because it is a base that dissolves in water and releases bicarbonate ions, thereby increasing the alkalinity without significantly altering the pH.

When considering the other options, calcium carbonate is primarily used to increase calcium hardness and can help raise alkalinity, but its effectiveness in directly increasing total alkalinity without significantly affecting pH is less pronounced compared to sodium bicarbonate. Potassium chloride and magnesium sulfate do not effectively raise total alkalinity; rather, they influence other water chemistry aspects. Potassium chloride mainly adds potassium ions and can affect salinity, while magnesium sulfate contributes magnesium but does not effectively raise alkalinity levels. Thus, sodium bicarbonate stands out as the most suitable option for this purpose.