Chlorine tablets vs granules for hot tubs

How each form works

Chlorine granules are measured into the water, usually with the pump running so they mix and dissolve. They act quickly, so a test a short while later shows the effect. That makes them good for setting the level after a refill and for topping up after a busy session.

Chlorine tablets dissolve slowly over days. In a hot tub they go in a floating dispenser, never loose on the floor of an inflatable, because a tablet resting on the liner can damage it. Some hot tub tablets are small multifunction tablets that combine chlorine with other agents. The dispenser's vents control how fast they dissolve.

Side by side

Getting the dose right

Whichever form you use, the aim is a free chlorine level in the range given on your test strips and product label, often around 1 to 3 ppm for hot tubs. Test before and after dosing until you know how your tub behaves. Our guide to reading test strips explains the colours.

Dose is always set by the product and your water volume. Use our water volume calculator to find your litres, then follow the label. Our chemical dosing page has a worked example.

Pool tablets are not hot tub tablets

Large chlorine tablets sold for swimming pools are often trichlor, which is acidic and very concentrated. They can push pH down quickly in a small volume of hot water. Use products labelled for hot tubs or spas, and check whether your tub's maker recommends a type.

Never mix different chlorine products or chlorine with bromine products in their dry form, and store all chemicals in a cool, dry place out of reach of children.

Note:Read the label before using any hot tub chemical. Add chemicals to water, never water to chemicals, wear gloves if advised, and keep products in their original containers away from children.

A simple routine using both

If tablets keep pushing chlorine too high, close the vents or remove the dispenser between uses. See how to lower chlorine if you overshoot.

1. 1

   After refilling, balance pH and alkalinity, then raise chlorine with granules to the label's start up level.

2. 2

   Set a floating dispenser with tablets to hold a baseline, if your maker allows one.

3. 3

   Test before each soak and add granules if chlorine is low.

4. 4

   After a busy session, add a granule dose and leave the cover open for a short while.

5. 5

   Adjust the dispenser vents if levels keep creeping up or down.

Which should you choose?

For most inflatable tubs, granules give the control you need, especially with irregular use. A tablet dispenser suits owners who soak often and want fewer top-ups. Keep it simple and stick with one chlorine type rather than swapping often. If you prefer bromine, see chlorine vs bromine.

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Frequently asked questions

Can I put chlorine tablets straight into my inflatable hot tub? No. A tablet sitting on the floor can bleach and weaken the liner. Use a floating dispenser or the maker's own dispenser.

Are multifunction tablets enough on their own? They can keep a baseline, but most owners still need granules after heavy use or a refill. Test regularly and follow the label.

Can I use pool chlorine in a hot tub? Products made for pools may be stronger or more acidic than suits a small, hot volume of water. Use spa products where you can.

Do granules or tablets affect pH? Some forms of chlorine affect pH more than others. Test pH regularly and correct it as needed.