Chlorine Type Cost-Per-PPM Comparator

Sticker price lies: a cheap jug of weak liquid and a pricey bucket of strong tablets don't deliver the same chlorine. We normalize every product to the honest unit — cost to raise free chlorine by 1 ppm in your pool — then rank cheapest first.

Step A — cost per lb of AVAILABLE chlorine
  Liquid:  pricePerGal / lbPerGal / (strength% / 100)
           lbPerGal = 9.7 (≥10% strength) or 9.0 (~6% household bleach)
  Dry:     pricePerLb × (100 / strength%)

Step B — scale to your pool
  costPerPpm      = costPerLbAvail × 0.00834 × (volume / 10,000)
  costForThisPool = costPerPpm × (FC raise ppm)
  0.00834 = lb available chlorine per 1 ppm per 10,000 gal

Step C — the side-effect each product hides (per 1 ppm FC)
  Trichlor  +0.6 ppm CYA      Cal-hypo  +0.8 ppm CH
  Dichlor   +0.9 ppm CYA (approximate — varies by formulation)
  Liquid    none

Why the side-effect column matters: trichlor often wins on raw $/ppm, but it adds cyanuric acid every dose — and once CYA climbs there is no chemical to remove it, only a partial drain-and-refill. That recurring cost is the "hidden cost" a $/ppm rank alone never shows. We flag a row when a single dose adds more than 5 ppm CYA or 8 ppm CH — a soft UX nudge, not a chemistry limit.

The 0.00834 lb/ppm/10k constant is the pure-chemistry conversion (1 ppm = 1 mg/L over 37,854 L), cross-checked against CleanPoolMath's published 10.8 fl oz of 12.5% liquid per ppm dose factor. Salt / saltwater generators are not included: their per-ppm cost is an amortization estimate (cell wear + electricity), not a price, so adding them would blur the exact liquid-vs-tablet comparison. The dichlor CYA ratio is approximate.

Sources: HomeownersHub (normalization to $/lb available chlorine, weight conversions); Aquatics International (CYA/CH side-effect ratios); CleanPoolMath (dose-factor cross-check). This is a comparative estimate, not a guaranteed price or a water-safety claim.