The preferred treatment for algae control is:

The preferred treatment for algae control in swimming pools is superchlorination, also known as heavy chlorination. This method involves raising the chlorine level significantly higher than normal operational levels, typically to around 10 times the usual amount. Superchlorination effectively destroys algae and other organic materials by ensuring that an adequate residual of chlorine is available to combat the growth of algae.

Algae thrive in environments where there is inadequate sanitization, so by employing superchlorination, the chlorine concentration can oxidize existing algae and help prevent future outbreaks. This process ensures that the chlorine can react with any compounds that may be contributing to the problem, allowing for a thorough cleaning of the pool water.

While other treatments such as copper sulfate can be effective in controlling algae, they often come with considerations such as staining and potential toxicity to aquatic life if used improperly. Similarly, quaternary ammonium compounds can be less effective in algae control compared to chlorine, particularly in outdoor settings where UV light can degrade their effectiveness. Draining and scrubbing the pool is certainly an option but is labor-intensive and does not address the water sanitation issue effectively.

In summary, superchlorination is favored due to its potency and the ability to quickly eliminate algae while improving overall water quality.