What should be done immediately after a heavy rain?

After a heavy rain, checking water levels and chemical balance is crucial. Rainwater can dilute the pool's chemistry, affecting pH levels, chlorine concentration, and other important water parameters. By assessing these factors immediately, pool operators can determine if any adjustments are needed to return the water to safe swimming conditions. This proactive measure helps to prevent potential issues like algae growth or bacterial proliferation from occurring due to imbalanced water chemistry.

Adjusting chemical treatments should always be based on actual measurements taken after rain, rather than automatically increasing chemicals without testing (as suggested in another choice). Draining the pool completely is generally not necessary unless the water is contaminated or there are other specific concerns, and stopping all maintenance activities could lead to neglecting essential checks that should be performed right after a rain event. Therefore, the best first step is to evaluate the situation through checking water levels and chemical balance.