Why that one pool keeps going cloudy

Every route has a pool that goes dull every few weeks while the log insists the chemistry is fine. It usually isn't a chemistry problem at all - it's a measurement problem, and this episode follows it all the way down to where you put the bottle in the water. Covered this week: how to draw a sample on a route - elbow-deep, at least 3 feet off a return, before you touch anything, and free chlorine tested first because it's the reading that degrades in a hot bottle. Why two techs on two testing methods produce a reading history nobody can read, and why cyanuric acid is where strips fail worst - a 40 ppm gap between a strip pad and a titration is a month of dosing to the wrong target. Then the readings that only go wrong over fifty visits: cal-hypo puts calcium in the water, dichlor puts stabilizer in, and liquid chlorine puts in neither but loses 25-30% of its strength in a hot truck bed over a Phoenix August. Which algaecide is worth carrying, and why copper is the one that leaves a mark on plaster. Cleaning filters off a per-pool pressure baseline instead of a calendar - and writing down the number after the clean, not just before. When to clean a salt cell, and when cleaning it is what's destroying it. Diagnosing sand in the pool from when the sand shows up. And the payoff: adding repair work in stages instead of all at once, and why a month of documentation you can export is what wins or loses your first commercial account.