Build a single-page widget that helps fish keepers figure out exactly how many gallons (or liters) of water to remove and replace during a routine tank cleaning.

The user enters:
- **Tank size** (total gallons or liters)
- **Desired water change percentage** (a slider from 10% to 90%)
- **Number of buckets** they plan to use (bucket size configurable, defaulting to 5 gallons)

The app instantly displays:
- **Total volume to remove** (in both gallons and liters)
- **Exact number of full buckets** needed and any leftover partial bucket amount
- A simple color-coded health indicator: green for 10–30% (safe weekly change), yellow for 31–50% (deeper clean), red for 51–90% (emergency change — fish stress warning message shown)

All calculations update live as the user adjusts any input. No page reloads, no backend — pure front-end math on one tidy page.