• Jess Court

How Much Chlorine To Add to Hot Tub First Time

If you’re thinking about purchasing a hot tub, one of the most important things you need to understand, with regards to its maintenance, is why, how much, and when you need to add chlorine to the hot tub water.

Chlorine is used in our daily lives because it kills germs and helps to keep us safe. However, it’s especially important for sanitising water as it reduces the likelihood of us ingesting or being exposed to illnesses.

The purchase of a hot tub is a significant investment, so you must take good care of it.

Why Do You Need to Add Chlorine to Hot Tub Water?

Chlorine is an essential part of your hot tub maintenance tool kit. It allows you to maintain and enjoy your spa. It is a chemical made from ordinary table salt, sodium hydroxide, and hydrogen.

It acts as a very efficient disinfectant and is used around the world to create the sanitised life we enjoy today. You’ll find it in a wide range of products, but one of the most popular is to help keep your water clean. You’ll find it in your drinking water, your pool, and your hot tub. All these rely on chlorine to protect you from waterbourne pathogens that could potentially make you ill.

Chlorine is a very safe thing to use, as long as you use it correctly. In your hot tub, it is one of two very effective chemicals that work in combination with the hot tub’s filtration system and cleaning schedule.

Hot tubs, by their very nature, are a giant, warm soup that contains all kinds of dirt, debris, organic waste, dead skin, oil, lotions, and hair products. If you don’t treat the hot tub water correctly, bacteria and free-floating germs will build up and take over and could make you very ill.

Why does a new hot tub require more chlorine?

Why does a new hot tub require more chlorine

When you fill your hot tub with fresh water for the first time you’ll need to add more than the usual amount of chlorine. This is because the hot tub water is yet to circulate through the filtration system.

When you add the chlorine for the first time, it will react with organics in the hot tub pipes and create compounds known as trihalomethanes. These can make you very sick if there are too many in your system. These trihalomethanes also react with hot tub chemicals and lead to chlorophenol formation. This will lead to off-gassing or chlorine odours when your hot tub is newly set up.

How Much Chlorine To Add to a Hot Tub for the First Time?

It is possible to purchase hot tub starter kits that conveniently have everything a hot tub owner needs to get started with their hot tubs.

However, it’s also possible to start hot tubs yourself, as long as you know how much to add for the first time.

How many chlorine tablets to add to a hot tub the first time?

As a general rule of thumb, you should add 1.5 times the amount of chlorine that is recommended for weekly chlorination for the size of your hot tub.

Chlorine tablets can be difficult to use for the first fill of your hot tub, but check the manufacturer's instructions. They are a very good source of information and will tell you whether chlorine granules or chlorine tablets are best suited for your spa water.

How much chlorine granules to add to a hot tub the first time

Typically, the amount of chlorine you would need to add to your hot tub for the first time is around one teaspoon of chlorine granules for every 100 gallons of fresh water.

Generally, you need to aim for a chlorine level of between 5 and 8 ppm. For any subsequent treatments, the free chlorine level should be between 2 to 4 ppm.

Whether you use chlorine tablets or add chlorine granules, the amount of chlorine you should use will depend on your hot tub’s size and shape, along with the amount of water it holds.

If you’re unsure about the amounts of chlorine granules or chlorine tablets to use, start with just one ounce for every 250 gallons of water. It that’s not enough, add more chlorine granules or chlorine tablets if it looks like bacteria is growing in your hot tub. A good chlorine level to start with is one ounce for every 100 gallons of hot tub water.

How to add chlorine to your hot tub?

To help you achieve the right chemical levels, you can pour liquid chlorine directly into your hot tub.

If you’ve decided to use chlorine granules, these should be dissolved in a clean plastic bucket first before adding to the water. You do this because it stops the chlorine granules sitting on the bottom of your hot tub. Granules that aren’t properly dissolved could discolour your water. Never add water to the chlorine, instead, fill the bucket with water first and then add the chlorine granules.

Add the dissolved chlorine granules to your hot tub while the pumps are running and add them near the water inlets. The water temperature should be at least 20° C. This will help with the distribution of chlorine in your spa water. if the water temperature is over 20° C you could sprinkle the granules directly into the water but this does run the risk of them not dissolving.

The addition of chlorine tablets is done by placing them in a floating chlorine dispenser and just letting them float around in the water.

A quick tip if you’ve got a new hot tub is to test the water in your home before you use it to fill up your hot tub. If you take a sample of your water to your hot tub dealer, they’ll be able to test the water and advise whether adding chemicals is neccesary and what chemicals will fit the water’s needs.

How long should you wait after adding chlorine to your hot tub?

When it comes to how long you should wait after adding chlorine to your hot tub there is no hard and fast rule. The best thing to do is check the levels. Ideally, you want the ppm chlorine levels to be around 5 or below before you step in for your first soak.

It’s been said that 20 minutes is long enough to wait, but to be on the safe side, wait at least 24 hours and test the chorine levels first.

How to understand if you’ve added enough chlorine to your hot tub?

Before you get into your hot tub, check the chlorine levels. This will tell you whether there is enough chlorine in the water. Using test strips or a digital test reader, check the free chlorine levels are between 3 and 5 ppm.

What If You Add Too Much Chlorine to Hot Tub Water?

If you add too much to your hot tub water, it can cause:

  • Skin irritation

  • Burning

  • Vomiting

  • Bleaching of materials

  • Eating away at synthetic fibres

How to tell if there is too much chlorine in your hot tub?

It’s a common myth that a “bleach smell” is an indication that chlorine levels are too high. In actual fact, the opposite is actually true.

If you can smell that unmistakable bleachy smell or strong chlorine odour, it means the chlorine in your hot tub has done its job.

The best way to tell whether the chlorine and pH levels are right is to test it. Don’t worry if there’s too much chlorine in your hot tub water, as there are several things you can do to lower chlorine levels in a hot tub.


How much chlorine to add to a hot tub after use?

This is a difficult question to answer exactly. How much chlorine you add and how often depends on your bathing habits, hot tub usage and how many gallons your hot tub holds. You should aim to maintain a level of between 3 and 5 mg/l at all times. You might find you need to add extra chlorine every day, every couple of days, or weekly. When adding the chlorine, to maintain 1mg/l you should add 2g per 1000 litres.

How much chlorine to add to a hot tub daily?

You shouldn’t need to add chlorine to your hot tub or worry about whether you need to raise chlorine levels every day. Instead, adding it twice or three times per week is better, depending on the frequency that you use your tub. The amount of chlorine to add depends on the level of the chlorine in the water which you can test using pH levels strip testers.

How often to add chlorine to a hot tub?

How often you should put chlorine in your hot tub depends on how often you use the hot tub and your bathing habits.

What does shocking your hot tub mean?

You’re shock dosing your spa when you add more chemicals than you would normally. When you want to shock dose your hot tub you’re typically adding a chlorine or non-chlorine chemical to kill anything that’s in the water. This chlorine shock treatment is also called oxidising. A shock dose removes any organic contaminants and chloramines (what is leftover when chlorine kills bacteria).



Jess Court

I'm Aqua Warehouse Groups Marketing Officer - overseeing all things news worthy in the hot tub industry, with tips and tricks that are bound to make a splash.

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