Which of the following increases if cyanuric acid is not present in outdoor pools?

When cyanuric acid is not present in outdoor pools, the rate of chlorine loss due to sunlight increases significantly. Cyanuric acid serves as a stabilizer for chlorine, protecting it from the degrading effects of ultraviolet (UV) light. When chlorine is exposed to sunlight without the presence of cyanuric acid, its efficacy diminishes rapidly because the UV rays break down free chlorine molecules.

With higher rates of chlorine loss, it becomes more challenging to maintain the desired level of sanitation in the pool, leading to potential water quality issues. Therefore, the absence of cyanuric acid results in a less stable chlorine concentration, which can compromise the pool's effectiveness in controlling algae and bacteria.

The other choices relate to different aspects of pool chemistry, but they do not directly correlate with the lack of cyanuric acid's stabilizing effect on chlorine.