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Hot Tub Chemicals: What You Need and How To Add Them

Matt Giovanisci, Founder and CEO of Swim University By Matt Giovanisci | December 29, 2023

There are a few hot tub chemicals you absolutely need to keep your water clean and clear. And there are a few that aren’t really necessary. It also matters what order you add each chemical to your hot tub. Adding the wrong chemicals in the wrong sequence can create cloudy water and render your chemicals ineffective.

So here’s a complete step-by-step walkthrough on which hot tub chemicals are definitely required, which ones you can skip, and in what order to add chemicals to your hot tub. You can watch the quick video below or keep reading for the complete guide on spa chemicals.

What Chemicals Do You Need for a Hot Tub?

If you want to keep your hot tub water balanced and avoid major problems like algae, bacteria, and biofilm build-up, you’ll need to have these hot tub chemicals on hand:

Before you add anything to your hot tub, you’ll need to test your water. You’ll want a good supply of test strips. Or, for more accurate results, you can use a liquid test kit. You can also take a water sample to your local pool and spa store if you want to test your water source for metals or other minerals. After you have your baseline readings, you can start adding your chemicals.

Here are the right hot tub chemical levels:

Ideal Hot Tub Chemical Levels
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1. Hot Tub Sanitizer

First, you’ll need to decide which type of sanitizer you want to use, usually chlorine or bromine. Each one has its pros and cons.

Chlorine

Many outdoor hot tub owners use chlorine to sanitize their water. It’s cost-effective, easy to add and manage and it’s an aggressive bacteria and algae killer. The downsides? That chlorine smell. Chlorine kills contaminants through oxidation. But as this chemical reaction occurs, it gives off waste products called chloramines that cause that smell.

If you can smell chlorine, it probably means your chlorine has been used up in your water and you need to add more. Remember, the proper chlorine level for a hot tub is 1 to 3 ppm, with 3 ppm being ideal.

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This granular, stabilized chlorine is fast-acting and quick-dissolving. You can add it directly to your hot tub water. Because this product contains CYA (stabilizer), it's best used in outdoor hot tubs that are exposed to UV rays.

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Bromine

Bromine doesn’t produce that chlorine-like smell in your hot tub. It also lasts longer than chlorine and has a lower pH, making it a little easier to keep the water balanced. And many hot tub owners prefer using it because it’s gentler on your skin. But it tends to work more slowly and it’s more expensive.

It’s also unstabilized. That means if you use it in an uncovered, outdoor hot tub, it’ll burn off pretty quickly under the sun. Bromine is best for indoor hot tubs, or hot tubs that aren’t in direct sunlight. The proper bromine level is 3 to 5 ppm.

Hot Tub Granular Bromine

These bromine granules dissolve quickly and can be added directly to your water. If you have an indoor hot tub, a covered hot tub or you want to avoid that "chlorine smell," this granular bromine is a great option to sanitize your spa.

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Mineral, Ozonator, and Salt Water Systems

You can reduce the amount of sanitizer you need to add to the water by installing a system like a mineral dispenser or Ozonator. Or you can purchase a salt water hot tub system. Be sure to check out our other in-depth guides on mineral systems and saltwater systems.

2. Hot Tub Shock

Hot tub shock is a great problem-solver and a must-have for regular hot tub maintenance. It helps refresh your existing sanitizer so it can work longer to prevent bacteria, algae, and contaminant build-up.

A weekly shock treatment using a non-chlorine shock (oxidizer) is a great way to help reboot your sanitizer and remove any used-up chlorine (a.k.a. chloramines. And if you see algae starting to bloom or you notice cloudy hot tub water, a chlorine shock can help remove contaminant buildup.

Oxidizer (Non-Chlorine Shock) for Hot Tubs

Also known as oxidizer, non-chlorine hot tub shock helps revitalize your chlorine or bromine so it can actively sanitize your water. Use an oxidizer at least once a week but ideally after each hot tub soak to keep your water sanitized.

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Chlorine or Bromine Shock?

Use either chlorine or non-chlorine shock. Non-chlorine shock is great for regular maintenance and you can use your hot tub soon after shocking it. But chlorine shock is more effective at killing algae or bacteria, so use this every other week or if you’re troubleshooting water issues. And it’s okay to use chlorine shock in a bromine hot tub.

If you want more information on what type of shock to use, check out our complete guide on How To Shock A Hot Tub.

Enhanced Chlorine Shock for Hot Tubs

A chlorine-based hot tub shock helps treat cloudy water, kill bacteria and algae, and remove contaminants after heavy hot tub usage. This formula also contains an oxidizer, which will help break apart any combined chlorine or bromine that's been used up in the water.

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3. Alkalinity Increaser, pH Decreaser, pH Increaser

One of the most confusing elements of hot tub water chemistry is pH and total alkalinity. pH measures how acidic your water is. And alkalinity acts as a buffer for pH, neutralizing incoming acid and keeping your pH from drastically changing. These two go hand-in-hand and affect each other whenever they change.

Your total alkalinity levels should be between 100 and 150 ppm (80 ppm is usually okay). The proper level for pH is between 7.4 to 7.6. Low pH can cause corrosion in your spa. High pH can cause itchy, dry skin and burning eyes.

There are a lot of products out there designed to raise or lower both pH and alkalinity all at once. But it’s important to have chemicals on hand that do one thing at a time.

Because this part of water chemistry can feel so complex, we have multiple guides:

  1. How to Raise Hot Tub pH
  2. How to Lower Hot Tub pH
  3. How to Raise Hot Tub Alkalinity
  4. How to Lower Hot Tub Alkalinity

4. Calcium Hardness Increaser

If you live somewhere with hard water, you may get calcium deposits on faucets and showerheads. But you actually want some of that hard water in your hot tub. If your hot tub water is too soft, it can eat away at your hot tub shell, pipes, and other parts. That’s why a calcium hardness increaser is so helpful.

Your calcium hardness levels should be between 175 and 250 ppm. Unfortunately, if your calcium hardness levels are too high, the best solution is to drain your hot tub, scrub it, and start over with fresh, filtered water. That’s why it’s important to add calcium hardness increaser a little at a time.

5. Hot Tub Line Flush Cleaner

Over time, the plumbing inside your hot tub can begin to accumulate mineral deposits, dirt, and grime. The only way to get rid of that build-up is to use a line flush cleaner and then drain your hot tub.

You’ll want to flush the plumbing and drain your spa every 3-4 months. And if you’ve never done that before, be sure to check out our complete walkthrough on how to drain and clean your hot tub.

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6. Optional Chemicals

Depending on your hot tub, here are some other helpful chemicals to have on hand:

How to Add Chemicals to Hot Tub Water

Adding the right chemicals in the right order can prevent cloudy water, slimy surfaces, and nasty hot tub smells. And if it’s the first time you’re starting up your hot tub, it’s extra important to add them in the correct sequence. Luckily, all the chemicals you need to start up your hot tub are the same ones we mentioned before that you need to maintain your spa throughout the year.

You can watch this video tutorial or keep reading for the step-by-step guide on how to add chemicals:

Before you start adding any chemicals to your spa, you’ll want to know how many gallons your hot tub holds. This will help you add the correct amount of chemicals to your hot tub. You can find your hot tub’s volume or water capacity in your owner’s manual or with a quick Google search.

Here’s how you’ll be adding chemicals to your water:

  1. Add chemicals directly to your hot tub water. Measure out your chemicals, then add them one at a time to the surface of your hot tub water.
  2. Wait at least 20 minutes before adding the next chemical. Keep your jets running and your air valves off to help your chemicals evenly and quickly disperse. You’ll want to make sure each chemical is completely dissolved before adding the next one.
  3. Keep your cover off. You’ll want your hot tub cover removed so chemicals like chlorine can “off-gas.”
  4. Be safe. Use gloves, goggles, and a mask when handling chemicals. And keep your chemicals separate before adding them to your tub. Mixing chemicals outside of your water can be dangerous and less effective.

What Order Do You Add Hot Tub Chemicals?

Before adding chemicals, test your water. If this is your very first time filling up your hot tub, you may want to use a more comprehensive test kit to measure calcium hardness or metals like iron and copper.

Tip: Filling up your hot tub with a hose filter can help remove impurities like metals and calcium before they get into your spa.

Next, heat up your spa until the water temperature reaches 80 degrees Fahrenheit or 30 degrees Celsius. The hot water will disperse your chemicals more effectively. And run your jets on low, turn off air valves, and keep your cover off of your hot tub.

Finally, it’s time to add your chemicals one at a time, waiting at least 5 to 15 minutes between each chemical before retesting. Here’s the step-by-step sequence we recommend for adding chemicals to your hot tub:

1. Add a Metal Sequestrant or Stain Preventer

If you need to add this to your water, do so before adding any other chemicals. This neutralizes metals in the water before they can stain your hot tub or harm your equipment.

2. Add Alkalinity and pH Increaser or Decreaser

Your pH helps your sanitizer work more effectively. Alkalinity helps prevent fluctuations in pH, so it’s important to adjust this level first. Alkalinity and pH go hand-in-hand, so adjusting one can affect the other.

That’s why it’s important to add your chemicals one at a time, wait for them to dissolve, and then retest your water. Remember, you can always add more, so don’t overdo it. Start with a few tablespoons if your levels are only a bit off.

And after adding each chemical, let them circulate for at least 20 minutes, then retest your water.

3. Add a Sanitizer (Chlorine or Bromine)

Now’s the time to add your chlorine granules or liquid bromine directly to the water. You can also use bromine tablets in a floating dispenser system. As always, start with a smaller amount of sanitizer, test your water, and add more if necessary.

Bromine does not dissolve as quickly as chlorine, so you’ll need to wait a bit longer to retest these levels. And if you’re using bromine tablets in a floater, this can take several days to disperse in your water before you get a proper reading.

If you’re using chlorine to sanitize your hot tub, we recommend using dichlor granules over trichlor tablets. It’s easier to control your dosing with granules compared to tablets. And trichlor can damage your hot tub’s acrylic shell.

4. Add Calcium Hardness Increaser

These levels do more damage in the long run, like eroding parts in your hot tub parts, so you can wait until your water is sanitized and balanced before adjusting your calcium hardness. Your calcium hardness levels should be between 175 and 250 ppm.

If you need to raise your levels, add a calcium hardness increaser. If your calcium hardness levels are too high, the best solution is to drain your hot tub, scrub it, and start over with fresh, filtered water.

Do You Need to Add Shock after Filling a Hot Tub?

You actually don’t need to add any spa shock right at this stage. Shock helps kill contaminants and remove compounds that build up over time. But because your hot tub is full of fresh water, and you don’t have any build-up of contaminants, you don’t need to add shock right away.

Tip

Frequently Asked Questions About Hot Tub Chemicals

Looking for more help adding chemicals to your hot tub? Here are some common questions and answers.

Can you go in a hot tub without chemicals?

It’s not safe to soak in a hot tub without chemicals. That’s like getting into a bathtub after someone else has used it!  A hot tub without chemicals is the perfect breeding environment for bacteria, algae, and contaminants. Just like a swimming pool, you’ll need to keep your spa water sanitized and balanced. If you’re the very first person to get into a  freshly filled hot tub, you might be okay. But that water will get very nasty very quickly.

How soon can you use a hot tub after adding chemicals?

You’ll want to wait until your chemicals completely dissolve and your water levels are adjusted correctly before using your hot tub. This means waiting at least 20 minutes after adding chemicals before soaking in your hot tub. And if you’ve just added chlorine shock, you’ll need to wait even longer.

How often should you change the water in your hot tub?

You should drain and refill your hot tub every 3 to 4 months. This is the chance to remove biofilm and build-up that gets stuck in your plumbing and can contaminate your water. Use a line flush cleaner and then drain, clean, and refill your hot tub with fresh water.

Is chlorine or bromine better for sanitizing a hot tub?

Many spa owners choose bromine over chlorine. It can cost a little more, but it lasts longer in your water and is very effective at killing bacteria at high temperatures. You’ll also avoid that chlorine-like smell caused by chloramines.

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Matt Giovanisci, Founder and CEO of Swim University
Matt Giovanisci is the founder of Swim University® and has been in the pool and spa industry since 1993. Since then, his mission is to make pool and hot tub care easy for everyone. And each year, he continues to help more people with water chemistry, cleaning, and troubleshooting.
Save Time And Money With Our FREE Hot Tub Cheat Sheet
Download this FREE printable cheat sheet to keep your hot tub clean and clear. You’ll never worry about your hot tub again with this easy-to-use guide.

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