Spa & Hot Tub Water Care
Hot Tub & Spa Chemical Dosing Calculator
Calculate precise dosing in teaspoons, tablespoons, fluid ounces, and grams for 300 to 1,000 gallon hot tubs, spas, and inflatable jacuzzis.
Spa & Hot Tub Dosing Engine
Precise small-volume chemical dosage
400 gal
Required Dosage+3 PPM Boost
Spa Dichlor Granules
1 teaspoons
(~0.3 tbsp / 0.25 oz)
Recommended Spa Sanitizer
Use quick-dissolving Spa Dichlor or Bromine granules specifically formulated for high-temp hot tubs.
Check Spa Sanitizer Prices on AmazonSafety Tip:
Run spa jets with air valves turned OFF while adding chemicals. Leave the spa cover open for 15 minutes after shocking.
Spa Dosing Rule of Thumb
In a 400-gallon hot tub, 1 teaspoon (0.25 oz) of Dichlor granules raises Free Chlorine by approximately 3 PPM.
Dichlor Granules (tsp) = (Spa Gallons ÷ 400) × (Target FC − Current FC) × 0.33Related Water Balance Tools
Frequently Asked Questions About Hot Tub Chemicals
Clear guidelines for maintaining clean, safe, and odorless spa water.
For chlorine hot tubs, maintain 3 to 5 PPM of free chlorine. For bromine hot tubs, maintain 3 to 6 PPM of total bromine. Hot tubs require higher sanitizer levels than swimming pools due to warm water temperatures and higher bather loads.
Bromine is more stable in hot water (above 98°F) and creates less pungent chemical odors than chlorine. Chlorine is faster-acting and easier to shock.
To raise free chlorine by 3 PPM in a 400-gallon hot tub, add approximately 1 rounded teaspoon (0.25 oz) of dichlor (sodium dichlor) granules.
A standard rule of thumb for hot tubs is draining and refilling with fresh tap water every 3 to 4 months, or using the formula: Spa Gallons ÷ 3 ÷ Average Daily Bathers = Days between refills.