Two coupled steps. First the shock / SLAM target FC: when you know your cyanuric acid (CYA), we read the target straight off the published FC/CYA shock chart (CYA 50 → 20 ppm, CYA 80 → 31, CYA 100 → 39 — the chart cells, not a round CYA × 0.40, which over-shoots at high CYA), interpolating between cells. When CYA is blank we fall back to the algae-severity target (light 20 / dark 30 / black 30 ppm).

target FC = FC/CYA chart cell (CYA known)  ·  severity 20/30/30 (CYA blank)
FC gap    = max(0, target FC − current FC)
dose      = constant × (volume / 10,000) × FC gap × (reference% / your%)

Then the dose via the operator mass-balance: the product amount scales with your pool volume and the FC gap, and keys off the product's available-chlorine %. Reference constants — liquid chlorine 10.7 fl oz / 10,000 gal / ppm at 12.5%, cal-hypo 1.3 oz at 68%, dichlor 1.57 oz at 56% — flex inversely with the strength you enter, so a 6% jug needs roughly twice the volume of a 12.5% jug for the same FC raise.

This is one pour. A SLAM is iterative — you re-test 3–4×/day and re-dose the gap until three exit tests pass: overnight FC loss ≤ 1 ppm, combined chlorine ≤ 0.5 ppm, and clear water. We give you the target and the protocol; the multi-day tracking stays your job (nothing is saved). Cal-hypo raises calcium hardness and dichlor adds CYA with every dose — so for a stabilized pool, liquid chlorine is the SLAM default. If CYA is over ~70 the chlorine demand is impractical; drain and dilute first.

Sources: PoolChemTracker — FC/CYA Chart (target cells); My Pool Calculator — Pool Shock Dosage (CYA-aware dose + cal-hypo constant); The Pool Nerd — Pool Shock Calculator (severity targets); PoolToolkit / TFP convention (SLAM exit criteria). Dichlor constant is a mass-balance derivation, spot-checked at build.