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  • Writer's pictureAqua Warehouse

How Much Chlorine To Add to Hot Tub First Time

Updated: Jan 4, 2023

Are you thinking about purchasing a hot tub? One of the most important things you must understand about looking after your new hot tub is why, how much, and when you need to add chlorine to the water.

Chlorine is used in our daily lives because it helps kill bacteria and keeps us safe. It's an effective water sanitiser, which is important because it reduces the likelihood of being exposed to bacteria.

The purchase of a hot tub is a significant investment, so you must take good care of it. And that means using chlorine to keep the water clean.

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

Chlorine is a chemical made from ordinary table salt, sodium hydroxide, and hydrogen. But when used as a sanitiser, it allows you to maintain tub/spa water clean. Chlorine is essential for any hot tub/pool/spa maintenance schedule because it's a very efficient sanitiser.

Chlorine is used in a wide range of products to help keep water sanitised. It's in drinking water, swimming pools, spas and hot tubs. All these rely on chlorine to protect users from waterborne pathogens that could cause illness.

Chlorine is safe to use, provided you use it correctly. It's one of two very effective chemicals that work with the tub's filtration system, cleaning the water and helping maintain the correct water chemistry.

Hot tubs are like a giant, warm soup that contains all kinds of dissolved solids, dirt, debris, organic waste, dead skin, oil, lotions, and hair products. If you don't treat the water correctly, bacteria and free-floating germs will build up. And that 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 new hot tub with fresh water for the first time, you'll need to use more than the usual amount of chlorine. Why? Because you must let the hot tub water circulate through the filtration system.

When adding chlorine for the first time, it will react with organics in the tub's pipes and create compounds known as trihalomethanes. These can make you very sick if too many of them are in your system. Trihalomethanes can also react with other chemicals, causing chlorophenol. The result is 'off-gassing' or chlorine odours when your hot tub is first set up.

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

You can purchase hot tub starter kits that conveniently have everything a hot tub owner needs to get started and do regular hot tub maintenance.

The question is how much chlorine to put in your hot tub before using it 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 put 1.5 times the amount of chlorine recommended for weekly chlorination for the size of your tub.

Chlorine tablets can be awkward for the first fill of your hot tub if you are unsure of how many to use. Check the manufacturer's instructions. They are an excellent source of information and will tell you whether chlorine granules, chlorine tablets, or liquid chlorine are best suited for your spa water.

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

Typically, the amount of chlorine you need to put in 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 subsequent treatments, keep free chlorine levels between 2 and 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, shape, and amount of water it holds.

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

How to add chlorine to your hot tub?

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

If you decide to use chlorine granules, pre-dissolve them in a clean plastic bucket before pouring the mix into the tub. This stops the chlorine granules from sitting on the bottom of your hot tub. Granules that aren't fully dissolved could discolour the water. Never add water to the chlorine; instead, fill the bucket with water first and put the chlorine granules in the water.

You should pour the dissolved chlorine granules into your hot tub near the water inlets. It's best to do this while the pumps are on. 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, try sprinkling the granules directly onto the water, but this runs the risk of them not dissolving.

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

A quick tip if you just got a new hot tub is to test the water in your home before you use it to fill up your tub. Take a water sample to your hot tub dealer so they can test the water and advise whether adding chemicals is necessary and what chemicals you need.

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

After adding chlorine to your hot tub, there is no hard and fast rule for how long to wait before using it. The best thing to do is check the levels. Ideally, you want the chlorine levels to be around 5 ppm 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, leave it at least 24 hours and test the chlorine levels before entering the tub.

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 put too much chlorine in 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” indicates high chlorine levels. In fact, the opposite is 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 correct is to test them. Don't worry if there is 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/litre at all times. You might find that you need to add extra chlorine daily, every couple of days, or weekly. When adding the chlorine, to maintain 1mg/litre you should add 2g per 1000 litres.

How much chlorine to add to a hot tub daily?

You shouldn't need to put chlorine in your hot tub or worry about adjusting chlorine levels daily. Instead, test levels twice or three times per week, depending on how often you use the tub. To raise chlorine levels, the extra chlorine needed depends on how much chlorine is already in the water. You can test this using pH level 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?

Shock dosing your spa is when you put more chemicals in the water than you would normally. When you want to shock-dose your hot tub, you typically add chlorine or non-chlorine chemicals to kill anything waterborne. This chlorine shock treatment is also called oxidising. A shock dose removes any organic contaminants and chloramines (what is left 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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