Fundamentals
Core water chemistry concepts every pool owner needs to understand.
Articles
Pool safety and clarity depend on four core measurements working together. This guide explains what each one does and why they must all be in range.
Balanced water neither corrodes surfaces nor deposits scale. This guide explains the Langelier Saturation Index and how to adjust your chemistry to stay in range.
Free chlorine, pH, total alkalinity, and calcium hardness are the four tests that tell you everything you need to know about your pool water safety.
Hot tubs use the same chemistry as pools but with tighter ranges, smaller margins, and much faster chemical depletion due to heat, jets, and small volume.
Higher water temperature speeds up chlorine consumption, shifts pH upward, and increases the risk of calcium scaling — all at the same time.
Regular testing catches problems when they are cheap to fix. Skipping tests allows chemistry to drift into territory that damages equipment, harms swimmers, and costs far more to correct.
A newly filled or freshly plastered pool needs a different chemistry sequence than reopening an existing pool for the season. This guide follows the staged, day-by-day start-up procedure published by the National Plasterers Council (NPC) via the Pool & Hot Tub Alliance (PHTA).
Indoor pools face a chemistry problem outdoor pools don't: without sunlight to break down chlorine, stabilizer becomes unnecessary and even counterproductive, while chloramine vapor and rising pH become the dominant issues instead.