Chemistry 101: Hot Tub Chemicals Explained

If you’re the type of person who struggles to keep house plants and sea monkeys alive, you may be somewhat anxious about playing ‘mad scientist’ with your hot tub, especially given the range of chemical concoctions promoted to new owners.

Never fear! The team at Hot Tub Addict is here to help with hot tub chemicals 101 – everything you need to know in the world of sanitizers, clarifiers, and more. 

Understanding Your Start Up Chemicals

The first big milestone in your hot tub chemical journey is its start-up. Just like a rocket lift-off, this is the bit you’ll really want to get right to make the subsequent journey to Destination Relaxation as smooth as humanly possible. There are three key chemicals you’ll find yourself using in this crucial phase:

pH Up: 

All your spa pH pamphlets may be giving you flashbacks to chemistry class, but don’t drop out of Hot Tub High just yet! Getting the right pH level in your tub is important, and luckily ‘pH Up’ chemicals are here to help.

If your water is sitting too low on the pH scale, it’s going to be acidic like vinegar. It will corrode metal equipment in your tub and irritate your skin. Water with a high pH will also cause chlorine to dissipate more quickly, so maintaining a good pH level is also essential for helping other hot tub chemicals do their job.

pH Up chemicals, also called pH Rise and pH Increaser, are most commonly made of soda ash (sodium carbonate) and raise the pH of your hot tub, helping you to reach that 7.4-7.6 pH sweet spot. Getting this balance right in the start-up phase is crucial, but pH is one of the things you’ll need to check regularly – at least 2-3 times per week.

If you neglect to balance out a low pH level with pH Up chemicals, you could be facing a corroded heater element, skin irritation, and off-balance hot tub water that just isn’t safe for you and your family to enjoy. Water with a low pH level increases your chances of contracting hot tub folliculitis or Legionnaires disease, so pH me up, Scotty!

pH Down: 

Just like a pH level that’s too low, a test strip showing high pH is also cause for action. If your pH is too high then your water is too basic, or alkaline, and will be dry like baby powder. This can lead to scaling on the tub’s surface and make the water cloudy. It also means the chlorine in your tub won’t kill pathogens as effectively.

pH Down to the rescue! This addition to your tub will lower the pH level, most commonly using muriatic acid, also known as hydrochloric acid. But beware the knock-on effects of using pH Down (aka pH Decreaser) chemicals: they can cause your Total Alkalinity levels to drop too.

Alkalinity Plus:

Often hot tub newcomers can be confused by the difference between pH and Total Alkalinity (TA). The distinction is less technical than you may fear. While pH shows on a scale how alkaline or acidic the water is, TA is a figure showing the total concentration of alkaline substances in your water. In other words, TA is a measurement, not a spectrum. The ideal range of total alkalinity is between 80-120ppm, depending on the type of chlorine you put in your hot tub.

There are a number of alkaline substances found in water, largely carbonates, bicarbonates and hydroxides. They help to neutralize acids in the water, and therefore have an impact on pH.

Low alkalinity is the more problematic of the high/low conundrum. Low TA can lead to extreme fluctuations in pH, which can have major effects on your hot tub’s appearance and water health. High alkalinity is problematic too – it can cause persistently high pH levels than can take a lot of effort to rectify, and to high calcium levels, cloudy water, and mineral build-up inside the spa.

Alkalinity Plus is your go-to chemical for a tub with low TA. But take care when you use it, and test your water again after 6 hours – the addition could cause your pH level to rise significantly. It’s a tightrope, but one worth walking!

Sanitizers – The Bacteria Busters

Your hot tub’s sanitizer is one of the most critical chemicals in your arsenal of tools, and one you should take time choosing.

Sanitizers are powerhouses that kill bacteria and purify water – exactly what you need to have a pleasant bathing experience! Think of them as your go-to for disinfecting your tub. Sanitizers banish dirty microorganisms and save you from bacteria, viruses and yeasts that may be lurking in the depths.

There are only a few chemicals recommended as primary hot tub sanitizers by the Center for Disease Control: chlorine, bromine, and a few mineral sanitizers (but only when used with an oxidizer). Take a look at the two most common, and see which you think will best suit your circumstances:


Most hot tub owners and spa professionals recommend chlorine as their sanitizer thanks to its relatively low price-tag and effectiveness when used at the right levels. Chlorine works best in conjunction with mineral sanitizers, helping to burn off dead organic matter and preventing cloudy water, but does require daily maintenance to balance and maintain.

While there are a number of chlorine products suitable for swimming pool maintenance, Dichlor is the ‘gold standard’ for hot tub sanitation. It’s best to use dichlor in granular form rather than large pellets (these can take too long to get working and may damage acrylic). Avoid using trichlor tablets, calcium hypochlorite or sodium hypochlorite in your spa, as these forms of chlorine are less effective and can be harsh on your tub’s parts.


Bromine is a common alternative to chlorine as a hot tub sanitizer. In some cases it can be easier to manage because it can be purchased in tablet form and added to a floating brominator. This method helps your tub get continuous sanitation, and avoids the extra maintenance that chlorine demands.

Bromine ionizes nasties in your hot tub, and unlike chlorine, which dies off as it attacks bacteria, bromine keeps active and working for a lot longer – meaning less maintenance and less product used. Many people also find bromine’s odor less potent than chlorine, and it can be gentler on sensitive skin.

That said, many spa owners are unaware that Bromine is composed of up 80%+ chlorine which is completely at odds with those who claim they use bromine simply because they are allergic or hyper-sensitive to chlorine.

Bromine has its downsides too. It can dry out skin more than chlorine does – especially for those who already suffer from eczema. It also degrades when exposed to sunlight and can discolor any jewelry you leave on when in the spa. And finally, many spa professionals claim Bromine can much harsher on the plumbing system, jets and related plumbing parts.

Chlorine vs Bromine is billed as the ‘age old hot tub debate’, but that may be overblowing what is ultimately a case of personal choice. Weigh up the physical effects and maintenance requirements of the two and see what suits you best.

Water Conditioners and Clarifiers – The Everyday Hero

Alongside your normal pH and alkalinity checks, there are extra measures you can take to keep your water crystal clear and smooth. Conditioning and clarifying your hot tub once every week can improve your pump and jet performance, and most importantly minimizes the build-up of bio matter.

Biofilm is the hot tub ‘gift’ that can keep on giving, so stocking up on the right weekly maintenance chemicals can go a long way toward combatting the biofilm monster and ensuring a healthy and happy hot tub.

Think of your conditioner as like topping up the oil in your car. You can pH test and sanitize all you like, but if you don’t use a conditioning product weekly, your hot tub isn’t going to look, sound, or smell as slick as it could.

Check out  Bio Ouster or  Hot Tub Serum and add one to your chemical cupboard. When you slip into your silky-smooth hot tub water you won’t regret it!

Other Chemicals – For When You Need A Specialist

  • Anti-foam – pull this off the shelf if you’ve let your maintenance schedule lapse a little and find yourself with a big outdoor bubble bath where you left your hot tub! Foam can be caused by washing soap residue or fabric softener in your swim suit, or the oils in body lotions, hair gels, make up products, and even your own skin!

Adding an anti-foam product will help dissolve the foam and get the water clear again, but as always, prevention is key!

  • Mineral & scale inhibitor – this is your go-to when your tub is suffering a scale build-up, usually caused by high calcium levels in your water. By adding some mineral and scale inhibitor, you can help prevent and remove scale and stains from your tub, prevent future scale build-up, and avoid cloudy water associated with high calcium levels.

Using this chemical can seriously extend the life of your heater, pump and filter – what’s not to love about that?!

  • Enzymes – these little fellows are your friends if you’re struggling to balance your water using key chemicals. They are useful at removing the food source of bacteria in the water, although it’s important to note that they are not sanitizers and should not replace your regular chemical sanitizer. They can, however, lessen the amount of chlorine or bromine you need to put in your tub by breaking down contaminants like body oils, sweat, and other nasties. Adding enzymes to your hot tub helps your water feel soft and can lessen the frequency of water balancing.

  • Plumbing purge – clean your pipes and renew your tub’s insides! Although your water may be looking and testing healthy, don’t forget that beneath the water there’s a web of interior plumbing circulating your water and pushing it out your tub’s jets. When sitting idle, your tub’s pipes can become clogged with lotions, sweat, and other contaminants, so sometimes you’ll need to treat the insides just like you do the outside!

If not properly maintained, the heat of your spa can create a nutrient-rich breeding environment for bacteria, and after a few months of perfectly fine operation, you may see black, brown or white specks floating from your jets when the tub is turned on. It’s a misconception that sanitizer will go in like a bomb and blast away all the bacteria in a hot tub – this just isn’t the case. Bacteria form colonies in the spa’s plumbing system, create an ‘outer shell’ to protect themselves, and become resistant to sanitizers. Using a plumbing purge chemical every two to three months can reduce the build-up of these colonies and keep everything running smoothly. We recommend completing a spa plumbing purge 1-2 times per year.

Ready, Set, Get Wet! 

There is certainly plenty to know about chemicals before taking the plunge into your new tub, but don’t be overwhelmed by all the products out there! Just remember there are four main types of chemical to be aware of:

  • Your start-up chemicals, which help to balance pH and total alkalinity
  • Your sanitizer – a crucial but consistent and easy to manage ingredient
  • Your weekly conditioning treatments – helping your spa reach its full potential
  • And the specialty chemicals that treat intermittent issues such as foam, scale, and blocked plumbing.

Think of your shelf full of chemicals like ingredients in your favorite cake. It’s all about reading the recipe, taking care with your amounts, and then, when it’s all done right, enjoying the result.