Use 8-12 ounces of chlorine shock for a 400-gallon hot tub

A 400-gallon hot tub requires 8-12 ounces of granular chlorine shock (sodium dichlor) per treatment, depending on usage and contamination. Shock weekly or after heavy use to maintain water clarity and sanitizer levels. Always pre-dissolve granules and follow product instructions for safety.

Key Factors Affecting Shock Dosage

  • Water condition: Cloudy or foul-smelling water needs 12 oz (double dose).
  • Usage frequency: Heavy use (4+ people) requires shocking after each session.
  • Shock type:
    • Chlorine (sodium dichlor): 8-12 oz (most common).
    • Non-chlorine (MPS): 4-6 oz (oxidizes contaminants without raising chlorine).
  • Temperature: Hotter water (100°F+) depletes sanitizer faster-shock more often.

Step-by-Step Shocking Process

  1. Test water: Use strips to check chlorine (ideal: 3-5 ppm) and pH (7.2-7.8).
  2. Pre-dissolve: Mix shock in a bucket of warm water (never add dry granules directly).
  3. Circulate: Run jets for 15+ minutes with the cover off to distribute shock.
  4. Wait: Avoid using the tub until chlorine drops below 5 ppm (typically 20-30 minutes).
  5. Retest: Confirm balanced levels before re-entering.

Shock Types Compared

Type Dosage for 400 Gal Chlorine Impact Best For Cost (Per Ounce)
Chlorine (Sodium Dichlor) 8-12 oz Raises chlorine levels Weekly maintenance, heavy contamination $0.20-$0.40
Non-Chlorine (MPS) 4-6 oz No chlorine boost Regular oxidizing, sensitive skin $0.50-$0.80
Liquid Chlorine (Bleach) 6-8 oz (6% solution) Rapid chlorine spike Emergency sanitizing $0.10-$0.20

Common Mistakes to Avoid

  • Over-shocking: Exceeding 12 oz can bleach liners or irritate skin.
  • Mixing shocks: Never combine chlorine and non-chlorine shocks-risk of dangerous gas.
  • Shocking at night: Sunlight degrades chlorine; shock at dusk or dawn for best results.
  • Skipping pre-dissolving: Undissolved granules can damage surfaces or equipment.

When to Shock Beyond the Weekly Schedule

  • After 5+ users in one session.
  • If water is cloudy, foamy, or smells like chlorine (indicates chloramines).
  • Following rain storms or debris contamination.
  • Before draining/refilling to reset water chemistry.