Solution for too low pH
The solution for too low a pH level is simply to add pH plus to the swimming pool. Depending on the current pH level, you need to add a certain amount of pH plus. The recommended dosing schedule is typically indicated on the packaging.
To measure the correct pH level, you can use a variety of test kits or strips. Digital units do the analysis for you. For test strips, you have to rely on your eyes, which makes them less suitable for people who are colour blind. The best, but also by far the most expensive, solution is a fully automated pH and chlorine dosing system.
The choice is yours!
See Also
Leslie's Dry Acid pH Down