What changed

Every change to a calculator, to a range it checks your reading against, or to a document behind one gets a dated line here, newest first. A revised label, a new edition of a code, a figure someone writes in to question: whatever moves, moves in public.

• September 21, 2026: added seven guides: how to lower pH, how to raise alkalinity, which chemicals never to mix, what cyanuric acid does, a green pool's first steps, opening and closing a pool each season, and how to read a pool chemical label. No calculator changed.
• September 19, 2026: launched with the pool salt, shock, chemical, pH and alkalinity, cyanuric acid, volume and LSI calculators and the pool chemistry log.