It would be great if you could just fill the pool with water and not have to worry about algae or bacteria growth. The reality is, you’ll need to add chemicals to the water to keep nasty contaminants at bay and make the pool environment a safe space.
Every time you swim, you leave behind body oils, traces of perfumes, shampoos, soaps, and other products in the pool. Your pool can also have twigs, leaves, and debris fly into the water, making the pool a solid breeding ground for all kinds of micro-organisms.
You will need to use sanitizers and oxidizers to disinfect the pool and add chemicals to balance the water attributes: pH, calcium, and chlorine levels. You may also want to add unique products like algaecides to really keep your pool clean.
However, it is important to remember that mixing certain chemicals directly is not recommended as the combinations may cause injury to swimmers.