The time it takes for a pool heater to heat a pool can range from eight to 48 hours, with an average of about 12 hours for the initial heating. For a more specific example, an average-sized 15,000-gallon pool may take six to 10 hours to heat up by 10 degrees. The exact duration depends on several factors, including the pool's size, the type and size of the heater, the starting water temperature, and the outside air temperature. It may take some trial and error to determine the precise time your specific pool takes to reach a desired temperature.

A black tarp will indeed heat your pool. Black absorbs more heat than other colors. This heat will transfer down to the water in your pool and help increase the temperature. It will not be extremely effective at raising the overall temperature, but it can help maintain the current temperature.

A pool chiller will take anywhere from 12 to 14 hours to lower your pool's temperature by 1 to 15 degrees. Most people tend to run their coolers overnight, but larger pools in warm climates take longer to cool. Choosing a chiller with the right capacity can help speed up the process.

Calcium lumps in a pool are calcium deposits that form when a pool's water parameters are not in the normal range. They can float around on the surface of the pool water, making it look and feel dirty. The most common causes of calcium lumps in pools are calcium hardness above 1,000 ppm, alkalinity over 120, and a pH over 7.8. Keeping your pool’s calcium levels, alkalinity, and pH levels within the normal, safe ranges is the best way to prevent calcium lumps and other problems, including damage to the pool surface.