Soak: Hot Tub & Spa Calc

Brand-aware hot tub chemistry. Bromine or chlorine, after-use top-ups, weekly shock — all the math, none of the upsell. Pay once. No subscription.

Pay once. No subscription, no ads, no account. Works offline.

Soak is the iOS hot tub chemistry assistant. Enter your test readings — free chlorine or bromine, pH, alkalinity, calcium — and get exact doses scaled to your tub volume. Brand-aware: pick the chlorine product on your shelf and Soak does the math.

Features • Brand-aware dose math for Cal-hypo 68%, Dichlor 56%, Liquid chlorine 12.5% • Bromine and chlorine sanitizer support, with sanitizer-specific target ranges • Test & Adjust: enter readings, get exact doses + plain-English advisories • After-Use Dose: scale top-up by people × hours in the tub • Weekly Shock guide with chlorine and non-chlorine (MPS) paths • Locale-aware metric/imperial units (grams/ml or oz/fl oz) • pH lowerer pick: dry acid or muriatic acid (31.45%) • Out-of-range advisories so a broken test kit doesn't dose you wrong • Universal app for iPhone and iPad

For hot tub owners who don't want to download a sales pitch. Bromine or chlorine, 250–500 gallon home spas, 950–1900 liter European tubs.

$3.99 one-time. No subscription, no ads, no account, no cloud.

Privacy: Soak collects nothing. No analytics, no accounts, no network requests. Your settings live on your device.