The work · Lesson 03 · 6 min
The water
A new tech learns three numbers before the rest of the chemistry. The other readings matter. They can wait until these three are a habit you do not skip when you are late.
What the three are for
Free chlorine is the sanitizer that is actually working. Combined chlorine is what is used up. If you only glance at a total, you can talk yourself into a pool that is not safe to swim.
pH is how the water sits against plaster, equipment, and people. Total alkalinity is what holds the pH still. Chase pH on a pool whose alkalinity is wandering and you will be back tomorrow, adding the other chemical.
Write it down, then stop
Test those three every visit. Write them every visit. A number you remember is a number you will argue about later, with a customer, or with yourself.
Add the chemical the test asked for, in the amount you measured. Then stop. More is not cleaner when the reading already landed where it belongs. The field guides on the phone go through each reading, including the ones you are leaving for later: cyanuric acid, calcium, salt, phosphates.