Chlorine Granules vs Tablets: Which is Better for Your Hot Tub?

The chemical used to kill bacteria in hot tubs is known as a sanitiser. Chlorine is the most popular sanitiser for hot tubs worldwide. Its popularity stems from its effectiveness, its lower cost compared to alternatives like bromine, and because most hot tub manufacturers recommend it as the default sanitiser. There are two main forms of chlorine: chlorine granules (a fast-dissolving powder) and chlorine tablets (slow-dissolving pucks roughly the size of a 50p coin). In this blog post, we’ll compare the key differences between the two and answer some of the most common questions about using these chemicals in your hot tub.

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Ease of Use

The obvious answer to this is that chlorine tablets are easier because you do not have to manually dose as often. From a dosing perspective, chlorine granules will take up more time as you have to manually dose the water more often. However, there are other elements that need to be considered too.

Chlorine granules offer the benefit of a bit more control. You have the ability to increase free chlorine levels much quicker by adding an increased dose. With tablets this is much harder due to the slow-dissolving nature of the chemical. In fact it is worth stating that many chlorine tablet users will use chlorine granules from time-to-time!

The other key point here is that chlorine tablets can have a negative impact on other levels in your hot tub, which creates more work overall. See 'Impact on water chemistry' below for more info.

Cost

Chlorine is generally very cost effective, especially when comparing to bromine and other sanitisers. There is not much of a cost difference between chlorine tablets and chlorine granules on a per KG basis. Comparing our Happy brand, 1kg of Chlorine Tablets is £17.99 and 1kg of Chlorine Granules is £14.99 however it is likely that 1kg of chlorine tablets would last longer than 1kg of granules. In both cases, buying in bulk helps save money. 

Control of Bacteria

Chlorine is an excellent sanitiser for hot tubs. It works quickly and effectively to keep your hot tub safe! Both chlorine tablets and chlorine granules are therefore very effective in killing bacteria. In both cases, the important point is that the chlorine level must stay between 3-5ppm. If the levels do not stay between these parameters, bacteria may be able to grow in the water. 

The benefit of chlorine tablets is that the tablets slowly dissolve over time so therefore you have a supply of chlorine entering the water over a period. Chlorine granules however must be added so there is a higher risk that levels may drop if the hot tub is not attended to, adding risk of bacteria growth. On the flip side, the slow-dissolving nature of chlorine tablets means that it takes time to build a free chlorine residual, which means bacteria has a chance to survive in your water if the free chlorine level is not 3-5ppm.

Impact on Bathers

This factor ties directly into the next one: the impact on overall water chemistry.

Chlorine tablets (typically made from trichloroisocyanuric acid, or trichlor) are naturally acidic — as the name suggests. As they slowly dissolve in your hot tub (often via a floating dispenser or skimmer), they gradually lower your pH and total alkalinity over time. If these levels aren't monitored and adjusted regularly, the water can become too acidic, leading to issues like itchy skin, stinging eyes, corrosion of hot tub components, or reduced sanitizer effectiveness. Read more about PH and Alkalinity here.

In contrast, chlorine granules (usually sodium dichloroisocyanurate, or dichlor) are much more pH-neutral (typically around 6–7, with minimal impact). This means they have little to no effect on your hot tub's pH or alkalinity, making water balance easier to maintain and reducing the need for frequent pH adjustments.

Another practical safety consideration with chlorine tablets is their physical form: they must be placed in a dispenser, floater, or skimmer — never directly in the water while people are using the hot tub. This is crucial because concentrated tablets can cause skin/eye irritation or chemical burns if handled improperly or if someone tampers with them. Always remove the dispenser before soaking to avoid direct contact or accidental over-chlorination.

With chlorine granules, there's no such risk — they dissolve quickly and completely when broadcast into the water, so no lingering concentrated product sits in your system.

Quick tip: For hot tubs, most experts (and many manufacturers) strongly prefer granules over tablets to avoid pH swings and potential equipment damage. Regular testing of pH (aim for 7.2–7.8) and alkalinity remains essential either way.

Impact on Water Chemistry/Components

As discussed above, chlorine tablets are acidic by nature but comparably, chlorine granules are relatively neutral in terms of PH. Lot of US hot tub manufacturers actually disapprove of chlorine tablets from being used in their hot tubs and threaten to void warranty if they are used. The reason for this is that the risk of someone throwing 5-10 chlorine tablets in a dispenser and doing nothing else is very high and this in turn can damage components. This won’t only affect bathers skin, eyes and hot tub components; there is also an impact on the efficiency of the chlorine in the hot tub. With PH being potentially very low as a result of the chlorine tablets, there is a risk that the chlorine cannot effectively kill bacteria, which could also put users at further risk.

The negative impact of chlorine tablets on PH level is one of the main considerations when choosing between chlorine granules and chlorine tablets. 

Comparison Chart

Verdict

At Happy Hot Tubs we have recommended chlorine granules as the best hot tub sanitiser for many years and we will continue to do so. This is mainly because of the harsh nature of chlorine tablets, combined with the lack of control for the user. If you do wish to use chlorine tablets and do so without any impact on components and bathers then see our blog: How to Use Chlorine Tablets in a Hot Tub. 

FAQs

Can I use chlorine granules AND chlorine tablets together?

Yes absolutley! If you are using tablets and need a boost then having a pot of chlorine granules will help you increase the free chlorine level quickly. Never mix chemicals directly.

How do I test Free Chlorine level in my hot tub?

Use Chlorine Test Strips to test for free chlorine level. Find out more about testing

Can I use non chlorine shock with chlorine granules and chlorine tablets?

Yes! Non chlorine shock is a very effective oxidiser and can be used with both or either chlorine granules or tablets. Never mix chemicals directly. Find out more about Non Chlorine Shock