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The hot tub chemicals you actually need

Short answer

A hot tub needs a sanitizer (chlorine or bromine), pH up and down, an alkalinity increaser, test strips or a kit, and a filter cleaner. Makers add shock, a metal sequestrant and a defoamer as needed, all made for spas, not pools.

Updated By the HotTubFinder research desk

Hot tub chemical types and what each does (product types, not brands)
TypeWhat it doesWhen
Sodium dichlor granulesSanitizerKills germs; nearly pH neutralTo hold your free chlorine range
BromineSanitizerKills germs; spent form has little odorOnly where your maker allows it
MPS (non-chlorine shock)OxidizerBurns off spent sanitizer and wasteWhen free chlorine is below total
pH increaserSodium carbonateRaises pHpH below range
pH decreaserSodium bisulfateLowers pH and alkalinitypH or alkalinity above range
Alkalinity increaserSodium bicarbonateRaises total alkalinityAlkalinity below range
Calcium increaserRaises calcium hardnessSoft fill water
Stain and scale (sequestrant)Keeps metals and minerals dissolvedEvery fill, then per label
DefoamerKnocks down foam for a whileSparingly; overuse clouds the water
Filter cleanerStrips oils and minerals from cartridgesMonthly soak
Biofilm (line flush) cleanerLoosens slime in the plumbingBefore draining

Which chemicals should you never put in a hot tub?

  • Pool chemicals. Master Spas says a spa is less forgiving than a pool and needs products made for spas.
  • Trichlor tablets, BCDMH and any compressed bromine or chlorine (Hot Spring).
  • Muriatic (pool) acid for lowering pH (Hot Spring).
  • Stabilized chlorine with cyanuric acid, in CDC's view; makers still list dichlor, so watch the cyanuric acid level.

How do you add chemicals to a hot tub?

Here the makers disagree, so follow your own manual. Hot Spring pours everything into the filter compartment with the jets on high for at least ten minutes, and says sprinkling chemicals on the surface can blister the shell. Master Spas says to spread them across the surface while the pumps run. Both say to leave the cover open afterward so the gas vents.

One product at a time, in the order alkalinity, pH, calcium, then sanitizer. See starting up a hot tub for the first fill.

How much to add

The product label sets the dose, by your tub's gallons.

Strengths differ between brands of the same chemical, so we don't print amounts. Test, read the label, add a little at a time with the jets running, wait, and test again. Your tub's gallons are in its manual or in our gallons and filter size table.

Common questions

What chemicals do I need for a hot tub?

A sanitizer (chlorine or bromine), pH increaser and decreaser, alkalinity increaser, test strips or a kit, and filter cleaner. Shock, a metal sequestrant and a defoamer as needed.

Can you use pool chemicals in a hot tub?

No. Master Spas says to use only chemicals made for spas, because a small volume of hot water reacts differently from a pool.

What order do you add hot tub chemicals?

Alkalinity, then pH, then calcium, then sanitizer, one at a time with time to mix between, as Bullfrog, Hot Spring and Master Spas describe.

Sources

4
  1. Hot Spring Highlife Collection owner's manual, 2026 d1oxc6ayqrhsgs.cloudfront.net · checked October 2026
  2. Master Spas Twilight Series owner's manual, 2026 masterspascdn.com · checked October 2026
  3. Bullfrog X Series owner's manual, 2026 bullfrogspas.com · checked October 2026
  4. CDC: Home pool and hot tub water treatment and testing cdc.gov · checked October 2026pH 7.0 to 7.8, no cyanuric acid in hot tubs, DPD kits more accurate than strips

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