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

By Matt Giovanisci | Updated: February 9, 2022

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 and in the wrong sequence can create a spa water nightmare.

So here’s a complete step-by-step walkthrough on which hot tub chemicals are definitely required, which ones you can skip, and how to add each chemical to your hot tub (and in what order).

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. Now after you have your baseline readings, you can start adding your chemicals.

Here are the right hot tub chemical levels:

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: chlorine, bromine, biguanide, minerals, or a saltwater system. Each one has its pros and cons. But the biggest debate is whether to use chlorine or bromine.

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If you want to learn about more sanitizer options, 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 provides a large dose of sanitizer to help ward off any developing water issues.

So if you see algae starting to bloom or you notice cloudy hot tub water, your hot tub shock will help. And a weekly shock treatment is a great way to help refresh your sanitizer levels and prevent issues down the road.

There are two types of shock: chlorine shock and non-chlorine shock. And they both have different applications:

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

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-and-hand and affect each other whenever they change.

Your total alkalinity levels should be between 100 and 150 ppm. And the proper level for pH is between 7.4 to 7.6. Low pH can cause corrosion in your spa. And 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 an entire guide on How to Balance Hot Tub pH (and with it, 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. 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.

We also make our own hot tub line flush cleaner at Swim University. You can check that out here:

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Optional Chemicals

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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:

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, 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 20 minutes between each chemical before retesting. Here’s the step-by-step sequence we recommend for adding chemicals to your hot tub:

1. Add metal sequestrant or stain preventer if necessary

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. Adjust alkalinity and pH

Your pH helps your sanitizer work more effectively. And 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, then retest your water. And 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. Adjust sanitizer levels, like 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. Adjust calcium hardness levels

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, like chloramines or bromamines. 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.

You can add a non-chlorine shock once a week when your hot tub is in use. This will help refresh your sanitizer levels. You can also use a chlorine shock if you’re experiencing issues with your hot tub water, like cloudy water or algae, or if your hot tub is in high use.

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.

Need More Hot Tub Maintenance Help?

Matt Giovanisci is the founder of Swim University® and has been in the pool and spa industry since 1995. 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.
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