Dichlor Dose
How Much Dichlor to Add to a Hot Tub
You need your tub volume, current free chlorine, target free chlorine, and dichlor strength. The needed dose rises as the FC gap and volume increase. Each dichlor dose also adds cyanuric acid, so repeat dosing should be tracked over the refill window.
Step-by-Step Method
- Test and record current FC.
- Choose a target FC for today's condition.
- Calculate FC rise as target minus current.
- Apply dichlor strength and volume to calculate dose.
- Record estimated CYA increase for that dose.
If FC rise is zero or negative, no dose is needed for that target.
Worked Example
| Tub volume | 420 gallons |
|---|---|
| Current FC | 1.5 ppm |
| Target FC | 4.0 ppm |
| FC rise | 2.5 ppm |
| Dichlor strength | 56% |
The final dose depends on the exact product assumptions. Spa Switch uses your saved profile values so the calculation stays consistent.
Why CYA Tracking Matters
Dichlor adds both chlorine and CYA. Repeated additions can move CYA to a point where many owners switch to liquid chlorine for ongoing sanitation.
The CDC notes that cyanuric acid is a chlorine stabilizer and that stabilized chlorines add it over time. Read the CDC context on cyanuric acid and chlorine stabilizers.
Use manufacturer and product-label guidance for your exact tub and sanitizer routine.
Calculate It in Spa Switch
Set Dichlor mode, enter current and target FC, and calculate. The result shows both dose and projected CYA for that dose. If unlocked, tap Save dose to build accumulated CYA history since refill.
Use Spa SwitchNext: read the CYA switch-point guide.