Should I Shock My Hot Tub After Refilling?

empty hot tub being filled up

Shocking a hot tub weekly is a necessity to keep the water correctly balanced. But sometimes it’s not clear when we’re supposed to shock it, so you may have wondered should I shock my hot tub after refilling?

Here’s what I know, having owned 4 hot tubs:

A hot tub should not be shocked after refilling as the purpose of shock is to reactivate the sanitizer. When it has just been refilled, adding sanitizer is sufficient. It is only after it has been used for a week or a high frequency of usage that shocking becomes necessary.

So shock’s whole purpose is to revitalize sanitizer that’s been used up combatting bacteria in the water. And when you refill, the water is still pristinely clear.

In this article, we’ll check out vital info around shocking that’ll help you keep your hot tub in the most sanitary condition. When should you add shock, what chemicals to use, what exactly does shocking do…

Let’s dive right in…

When should I add shock to my hot tub?

Ideally, shock should be added to hot tub water approximately 7 days following the previous shock or 7 days following a refill. But it can also be added after a day of extra heavy usage.

Shock is a “supplement” to sanitizers.

Therefore, it’s meant to be applied after the sanitizers have been added and the hot tub has been used for a week, or a few days, if there’s a high frequency of usage or a high bather load.

As people use the hot tub, they unwittingly introduce some contaminants into the water. Shocking helps remove those contaminants and kills off bacteria. It also restores the sanitizers to their original state, making them more effective.

I’ll share more about its value in a bit. Now, let’s check out how to shock the tub.

Remove the hot tub cover so that the water can be aerated. Then, check its pH level to make sure it’s correct.

After that, check that the chlorine level is between 7.2 and 7.6. If you’re using bromine, the ideal range is between 7.0 and 7.4. Ensure the water is circulating by turning on the jets.

Then measure out 1.25 oz. of chlorine shock per 400 gallons of water and add it to the water.

What if you prefer non-chlorine shock? Simply measure out 1/2 oz of non-chlorine shock per 400 gallons of water and add it to the water.

Leave the hot tub cover off for about twenty minutes. You can easily find out your hot tub’s gallon capacity in your owner’s manual.

But if you want a simple way to calculate the capacity of your hot tub, I give you the exact formula and 2 different methods in this recent article.

Just click that link to read it on my site.

What chemicals do I add to my hot tub after filling?

Sanitizer should always be added after refilling a hot tub. This can be bromine or chlorine, or an alternative. Then check both the alkalinity and the pH and add chemicals to adjust up or down as needed (if any change is needed).

The sanitizer has the job of disinfecting your hot tub water, and you have several options to choose from. They are:

  • Bromine
  • Chlorine
  • Biguanide
  • Minerals
  • Salt systems

Most people use either chlorine or bromine. Chlorine is cheaper, but it dissolves fast because it’s not able to do well in the heat generated by the water.

Bromine, on the other hand, is more heat-resistant, so it takes a longer time before it dissolves. But, it is a bit more expensive.

In addition to the sanitizers, you’d also need a chlorine-based or non-chlorine-based shock. You don’t use it immediately after filling, but once each week.

But before you apply the one you prefer (you can’t use both, but you can switch), the water’s pH and alkalinity have to be tested.

It’s vital to understand what pH and alkalinity mean because both interact with each other and also affect how effective the sanitizers can be and even your experience of soaking. So, it’s vital to get their levels right.

  • pH is a measure of how acidic water is.
  • Alkalinity is a measure of the water’s capacity to neutralize acids.

When you’ve tested the water and have added the sanitizer, how soon can you use the hot tub?

This is the theme of a recent article of mine. In it, I explained the danger of going into a hot tub where the chlorine level is above 3 parts per million.

Just click the link to read it on my site.

What does shocking a hot tub do?

Shocking a hot tub has three major functions: it kills bacteria, removes organic contaminants, and removes chloramines and bromamines, resulting in a reactivation of the sanitizers.

It makes them more effective and removes the buildup that regular sanitizers cannot.

With frequent use, the hot tub water gradually becomes filled with organic contaminants and microorganisms that are not only gross but could also cause diseases. Organic contaminants are stuff like dead skin cells, makeup, shampoo, lotion…

And, truth be told, the sanitizers are not enough to keep your tub in a sanitary condition because over time, they become less effective, as they’re overrun by the contaminants.

Shocking kills off anything that’s missed by your sanitizers.

Shocking involves applying an ample dose of oxidizer to the water. This helps in killing bacteria, removing organic contaminants, and reactivates sanitizers. It’s essentially using a large dose of oxidizer to “shock” the water to restore it to a clean state.

It makes sanitizers more active because the free chlorine or bromine that’s been suppressed through the formation of chloramines or bromamines are released and can now work freely in combating the debris and microorganisms.

Shocking removes chloramines and bromamines (both are one of the reasons hot tubs often smell).

Can you use a chlorine shock if you use bromine as a sanitizer?

Find out in a recent article of mine. In it, I explained it’s okay and that both should not be mixed in powder form.

Just click the link to read it on my site.

If I use tablets, should I add shock to my hot tub after refilling?

There is no need to shock a hot tub after refilling, even if tablets are used as sanitizer since the water is fresh and does not yet contain contaminants or sanitizer that has been depleted.

One of the benefits of using tablets is that the sanitizer takes a longer time to dissolve, which means the hot tub water can be used for a few more days or a week.

Tablets are designed to slowly dissolve in the hot tub water, and they can last for 3-5 days before there is a need to add more.

With fresh water, plan to wait about a week before you need to shock the water, unless a large number of people will use the tub so many times in the course of a few days. The general guideline is to shock after the water has been used for a week.

So, in most cases, simply adding tablets would be good enough for 3-5 days.

If you’re not yet sure of the difference between chlorine and bromine, you’ll find a recent article of mine highly helpful. It’s okay to switch from one to the other, but both should never be used together!

In the article, I explained, amongst other things, that both are sanitizers that are vital for hot tub maintenance. Chlorine is less stable in water relative to bromine, but bromine is a bit more expensive.

Just click the link to read it on my site.

Is hose water chlorinated?

Hose water is chlorinated because water provided by the local or city authorities is treated with chlorine. However, the levels will be insufficient to combat contaminants in hot tub water, so adding sanitizer is necessary.

But it’s vital to note that even though the water is safe for drinking, the fact that it passes through a hose might make it unsafe for drinking.

It’s safe for use in a hot tub because it will be treated before it is used.

However, the level of chlorine in it from the municipal authorities is too low for the water to be used as it is in a hot tub.

So, even though hose water is chlorinated, you’ll have to test its pH, alkalinity, and chlorine level. Then, add an appropriate amount of chlorine or bromine and then test it again before it’s suitable for use in a hot tub.

Say you’ve added chlorine or bromine to the hot tub water.

How soon can you use it afterward? That’s what I explored in a recent article of mine where I advised to wait for 30 minutes. I also shared how long you’ll need to wait when you’ve applied chlorine or non-chlorine-based shocks.

Just click the link to read it on my site.


Should you shock your tub after refilling it? That’s the theme of our exploration in this article.

We checked out a couple of vital pieces of info around when to shock a hot tub. We looked at what shocking does when to do it and the chemicals to use after refilling a hot tub.

We also explored if shocking is needed when tablets have just been added to the hot tub water. Lastly, we looked at whether hose water is chlorinated and what to do to use it.

Photo which requires attribution:

Filling it up! by Dave Parker is licensed under CC2.0 and was cropped, edited, and had a text overlay added.

Jeff Campbell

Jeff Campbell is a husband, father, martial artist, budget-master, Disney-addict, musician, hot tub lover, and recovering foodie having spent over 2 decades as a leader for Whole Foods Market.

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