Hot tub chemicals: what you actually need

A hot tub needs five things: a sanitizer (chlorine or bromine), a shock (oxidizer), pH increaser, pH decreaser, and test strips. Everything else is optional or only needed for specific problems. Buy products labeled for spas, follow the label for your tub's volume, and never mix chemicals together.

The essentials

Product	What it does	How often
Sanitizer: chlorine granules (dichlor) or bromine tablets or granules	Kills bacteria	Keep a constant level. Check 2–3 times a week.
Shock: non-chlorine (MPS) or chlorine shock	Burns off sweat, oils, and used-up sanitizer	About weekly and after heavy use
pH increaser (soda ash)	Raises pH	When pH is below 7.2
pH decreaser (sodium bisulfate, dry acid)	Lowers pH and alkalinity	When pH is above 7.8
Test strips	Tell you what to add	2–3 times a week

Sanitizer

Pick chlorine or bromine and stick with it. Chlorine targets 1–3 ppm free chlorine. Bromine targets 3–5 ppm. Chlorine is cheaper and acts fast. Bromine holds up better in hot water and has less odor. The full comparison is in chlorine vs bromine.

Shock

Shock is an oxidizer. It breaks down the waste that makes water dull and smelly. Non-chlorine shock lets you soak again soon after. Chlorine shock also sanitizes and is the right choice after heavy use or a water problem. See when and how to shock.

pH up and pH down

Hot tub pH drifts up over time because the jets drive off carbon dioxide. Most owners use more pH decreaser than increaser. The target is 7.2–7.8.

Often needed, depending on your water

• Alkalinity increaser (sodium bicarbonate). Needed when total alkalinity is under 80 ppm. Low alkalinity makes pH bounce around.
• Calcium hardness increaser. Needed when fill water is soft, under 150 ppm. Soft water foams and slowly attacks heaters and pump seals.
• Metal sequestrant or stain and scale control. Useful for well water with iron or copper, and for hard water above 250 ppm calcium.
• Filter cleaner. A monthly soak strips oils that a hose rinse leaves behind. This one is worth buying. See how to clean a hot tub filter.
• Line flush (pipe cleaner). Used before each drain to clear biofilm from the plumbing.

Problem solvers you may never need

• Defoamer. Knocks foam down for a few hours. It treats the symptom, not the cause.
• Clarifier. Clumps fine particles so the filter can catch them. Use only after sanitizer and pH are right.
• Enzymes. Break down oils and lotions. Helpful in a heavily used tub.
• Sodium bromide. Sets up a bromide reserve at the start of a fresh fill in a bromine tub.

What to skip

• Trichlor pool tablets. They are very acidic and too strong for hot tubs. They can damage covers, pillows, and heaters.
• Household bleach with additives such as scented or splashless types. They foam and leave residue.
• Bulk pool shock (calcium hypochlorite). It adds calcium and is dosed for pools. Most spa makers advise against it.
• Kits with ten bottles. Starter kits are fine, but you will use two or three products often and the rest rarely.

A simple weekly routine

1. Test the water with a strip.
2. Adjust alkalinity if it is outside 80–120 ppm.
3. Adjust pH to 7.2–7.8.
4. Top up sanitizer to range.
5. Shock once a week, with the cover off for at least 20 minutes.
6. Rinse the filter every week or two.

That routine takes about ten minutes. For target numbers in one place, use the ideal levels chart.

Storage and safety

• Store chemicals cool, dry, and out of the sun, with lids tight. Not in the equipment bay.
• Keep them away from children and pets.
• Add chemicals to water, never water to chemicals.
• Never mix two products together, in a bucket or in the scoop. Chlorine and acid make toxic gas. Different chlorine types can react violently.
• Use a clean, dry scoop for each product.
• Add chemicals with the jets on and the cover open, and leave the cover open for 15 to 20 minutes afterward.

How much to add

Doses depend on the product strength and your tub's volume, so follow the label for your gallons. Most hot tubs hold 250 to 500 gallons. Your volume is in the owner's manual or on the maker's spec sheet. If you are unsure, add less than you think, wait 30 minutes, and retest. It is easy to add more and tedious to undo too much.