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Used properly chlorine can be your best friend in maintaining hot tub water quality. We have compiled a list of the most Frequently Asked Questions about chlorine to help that friendship progress a little more smoothly.


Find out how to use chlorine to keep your hot tub water safe and clean.

Chlorine is an essential part of your tool kit for maintaining a healthy and enjoyable spa. As a hot tub owner, you’re probably already aware that chlorine can be added to your hot tub water in two different forms:

  • Chlorine Tablets
  • Chlorine Granules

But you may have wondered, does it make a difference whether I use chlorine tablets or chlorine granules in my hot tub? Does one form of chlorine work better than the other? Let’s find out!

Which is best? Chlorine Granules or Tablets?

Should I use Chlorine Granules in My Hot Tub?

The benefit of using chlorine granules is that they are quick to dissolve and relatively pH neutral. This makes chlorine granules ideal for shock-dosing on initial set-up with fresh water, or if the spa hasn’t been used for a period of time. Chlorine Granules will raise chlorine levels more rapidly than chlorine tablets.

Should I use Chlorine Tablets in my hot tub?

Chlorine tablets offer a more “hands-off” approach to maintaining your spa water. Chlorine tablets release chlorine slowly, making it easy to maintain a consistent level of chlorine in the water over a longer period of time. If you are going away for a few days or have limited time to sort out the water chemical levels, chlorine tablets are a good choice for you.


Is it easier to use chlorine tablets or chlorine granules in my hot tub?

It really depends on how you use the tub! If you don’t use your hot tub very regularly and need to shock dose often, chlorine granules may be more convenient for you. If you want to maintain a consistent chlorine level you will need to schedule adding granules to your spa – this may become a hassle for you. Regular spa users may find tablets more convenient. Getting the correct chlorine levels set initially may take some experimentation, but after that, as long as you make sure that you have replaced the tablets once they have dissolved away they are fairly hassle free.

How do I add Chlorine Granules to my hot tub?

You can add chlorine granules to your spa water simply by sprinkling them directly into the water (as long as the water temperature is greater than 20° C). However, this method does carry a risk! If the granules settle on the acrylic surface of your spa and do not dissolve this may cause damage which is very unlikely to be covered by the manufacturers warranty.

If the water temperature is less than 20° C, if you are unsure of the water temperature, or if you want to avoid potential damage to acrylic surfaces, then the best method is to pre-dissolve the chlorine granules in a clean plastic bucket. Never add water to the chlorine, fill the bucket with water first then add the chlorine.

Add the dissolved Chlorine Granules when the pumps are on, and near to the water inlets as this will aid the distribution of chlorine around your spa.

Don’t get carried away! You don’t want to over-chlorinate your water. So just add one dose at a time.

The Goldilocks zone – not too much, not too little!

How many Chlorine Granules should I add to my hot tub?

A little maths is required!

2g of Chlorine Granules will increase the chlorine level of 1,000 litres of water by 1mg/l (ppm).

If you are pre- dissolving your granules in a bucket of water you can follow this formula up to a maximum rate of 10g Chlorine to 1 litre of water. To be accurate you will need to know the volume of water in your hot tub. Alternatively, you can add a little chlorine at a time, allow it to circulate and then test and re-test until you achieve the chlorine level you are aiming for.

How do I know if I have added enough chlorine to my hot tub?

Before bathing, you should check the chlorine level is within the range of 3-5mg / l (ppm). You can check your free chlorine levels with test strips. If you want increased accuracy with your water testing, digital test readers are available.

How do I use Chlorine Tablets?

How do I add Chlorine Tablets to my hot tub?

The amount of chlorine released is controlled by adjusting the dial of a floating chemical dispenser. A little bit of trial and error might be needed at first to find the sweet spot on your chemical floater that maintains the desired levels of chlorine. However, once you have found the level that works for you it should be relatively easy to keep chlorine levels consistent.

How often do I need to replace chlorine tablets?

Chlorine tablets will typically erode over a period of 3-5 days, depending on the amount of water flowing over them.


I don’t want to use chlorine, are there alternatives?

You MUST use a water sanitiser!

Help! I’m allergic to chlorine!

A lot of people think they are allergic or intolerant to chlorine. For most people this isn’t the case. Water pH levels play a huge role in how comfortable we are in water. Water that is either too acidic or too alkaline will irritate our skin, eyes and sinuses. The water pH must be balanced and neutral for the sanitiser to work effectively.

Do I have to use chlorine in my hot tub?

No. You don’t have to use chlorine. But you do have to use a water sanitiser. For most people chlorine is the safest and most effective sanitiser to use in their spa. An alternative sanitiser is bromine.

How Can I Use less chlorine in my hot tub?

High levels of chlorine can be undesirable. The keys to maintaining safe and healthy hot tub water while using lower levels of chlorine as a sanitiser are:

  • Keeping pH levels balanced – ideally close to pH 7.2
  • Use AquaFinesse to eliminate bio-film

Why are pH levels important?

At a pH of 8, over half of chlorine added to your hot tub water is ineffective. At a pH of 7.2 chlorine efficacy rises to 90%. This means that 90% of the chlorine is actively available to kill algae and bacteria.

Why use AquaFinesse?

Biofilm is a type of slime that forms and provides a safe shelter for bacteria. A layer of Biofilm then allows bacteria to breed virtually unmolested by chlorine or any other sanitiser. AquaFinesse breaks this shelter down, thereby allowing smaller amounts of chlorine to be more effective.

My hot tub water smells strongly of chlorine what should I do?

Your hot tub water can start to smell when chlorine combines with organic waste (body fluids, dead skin etc). This waste and chlorine mixture then produces a compound called chloramine.

Chloramine gives off a strong chlorine odour and is often mistaken for too much chlorine. This smell is in fact an indication that the chlorine has been used up.

Shock treatment will breakdown chloramine. It can be easily removed from the water, freeing up the chlorine to work more effectively.


We hope you have found our guide to using chlorine in your hot tub or spa useful. Check out our other water quality blogs for more help maintaining your spa water quality, or take a look at our FAQs for the quickest way to find the answers you are looking for! Castle Hot Tubs are proud to be a member of BISHTA.



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