Hot Tub Time Machine

A mobile-friendly hot tub chemical tracker deployed on Cloudflare Workers with D1 database, at https://hot-tub-time-machine.tarek-rached.workers.dev/ . Track water chemistry test sessions, log chemical additions, and get dosing recommendations — all from your phone while standing at the hot tub.

Features

• Test Wizard — Per-test sequential flow (TA → Bromine → pH → Calcium) with session recovery, 15-minute retest timers, and dosing recommendations. When bromine and pH are both selected, bromine is read first, pH is fully fixed, then bromine is fixed — preventing bleach from skewing the pH reading.
• Drop-to-PPM Conversion — Automatic conversion for Taylor K-2106 titration tests (supports 10ml and 25ml sample sizes); pH uses a swipe slider with out-of-range <7.0 / >8.0 support
• Dosing Recommendations — Calculates chemical amounts based on current readings for a 330-gallon tub
• Dashboard — Status cards with urgency coloring (green/yellow/red), sparkline trends, and overdue test badges
• Maintenance Log — Track filter changes, water changes, and drain/refill events with sodium bromide reminders
• pH Enforcement — Soft auto-skip when bromine > 10 ppm (Taylor kit limit) with manual override

Tech Stack

• Runtime: Cloudflare Workers with static assets
• Framework: React Router v7 (framework mode) with SSR via @cloudflare/vite-plugin
• Database: Cloudflare D1 (SQLite)
• Styling: CSS Modules, light theme optimized for outdoor readability
• Testing: Vitest for chemistry unit tests
• Deployment: GitHub Actions → Cloudflare Workers via Wrangler

Development

npm install
npm run dev       # Local dev server with HMR
npm test          # Run chemistry unit tests
npm run build     # Production build

Chemistry

Configured for a 330-gallon hot tub using the bromine 3-step method with 7.5% disinfecting bleach and a Taylor K-2106 drop-based test kit. See docs/bromine-3-step-method.md for the full reference and docs/cheatsheet.pdf for the original printed cheat sheet this app replaced.

Test	Ideal Range	Cadence
pH	7.4 – 7.8	Weekly
Bromine	4 – 6 ppm	Weekly
Total Alkalinity	50 – 70 ppm	Every 3 weeks
Calcium Hardness	130 – 150 ppm	Every 3 weeks

Deployment

The app deploys to Cloudflare Workers automatically on push to main via GitHub Actions.

Required GitHub repo secrets

• CLOUDFLARE_API_TOKEN — Cloudflare API token with Workers Scripts:Edit, Workers Routes:Edit, D1:Edit, and Account Settings:Read permissions
• CLOUDFLARE_ACCOUNT_ID — Cloudflare account ID

Manual deploy

npm run build
npx wrangler d1 migrations apply hot-tub-time-machine --remote
npx wrangler deploy --config build/server/wrangler.json

Routes

Route	Purpose
/	Dashboard — status cards with urgency coloring, sparkline trends
/test	Test wizard — per-test sequential flow with session recovery
/settings/log	Combined timeline of test sessions and maintenance events
/settings/maintenance	Action buttons to log maintenance + drain/refill bromide reminder
/settings/reference	Static dosing tables, drop-to-PPM reference, test schedule