Should I Shock My Hot Tub After Refilling?

By Calvin | Last Updated: June 23, 2021 | Maintenance / Water Chemistry

You don’t need to shock your hot tub after refilling it because hot tub shock is mainly an oxidizer that reactivates the sanitizers being used in the water. Since you haven’t added any sanitizer to the water, there is no chemical or sanitizer to shock.

Draining and refilling your hot tub is a crucial part of your spa’s maintenance. When you drain your hot tub, you refill it with fresh water but the concern here is, the freshwater isn’t exactly “fresh.”

The freshwater you fill your hot tub with either from the tap or the well has a few dirt particles, metals, and debris in it. So you might ask yourself, “should I shock my hot tub after refilling?”

This post reveals more about shocking hot tubs including an expert tip to figure out when to drain and refill your hot tub. Let’s get to it.

You just drained and re-filled your hot tub, do you need to shock it? Let's see.

When Should You Shock Your Hot Tub?

You should shock your hot tub once per week during heavy use or once in two weeks during regular use. You should also shock the hot tub if the sanitizer level is low.

When should you shock your hot tub? You need to shock your hot tub once a week if you are using it often.

You need to shock the water when the water is getting dirty and the chlorine or bromine level is very low. This is the best time your hot tub will benefit from the shock. This means you don’t need to shock your hot tub when you refill it.

Alternatively, you can tell when you need to shock your hot tub by testing the water regularly. Whenever you discover that the chlorine or bromine level in the hot tub is low, you can shock the hot tub to reactivate the sanitizer.

The ideal chlorine level for a hot tub is between 1ppm and 3ppm. If the chlorine test result shows that you have less than 1ppm of chlorine in the water, you should shock the water.

For bromine, the ideal level is between 3ppm and 5ppm. If your bromine level falls below 3ppm, you should shock the water too.

Shocking the hot tub water should also be done whenever there is green water in the hot tub. Green water is hot tub water filled with hot tub scum, bacteria, and even algae. The water usually has a green color and leaves a green or brown tint on the shell. It also smells… eww.

How Does Hot Tub Shock Work?

Hot tub shock is a chemical that works by reactivating the hot tub sanitizer that is being used in the hot tub. The shock increases the sanitizer level in the hot tub and destroys hot tub scum and other contaminants in the water. 

How does hot tub shock work?

A misconception about hot tub shock is that when it is added to the water, it fights and kills all the hot tub scum and germs. Well, it does but not the way you think.

When you shock a spa, the shock you added is both an oxidizer and a sanitizer. It reactivates the sanitizer in the water and adds to it. This means that the sanitizer can battle the contaminants better. Think of it as the chlorine in your hot tub calling for backup.

So it’s not the shock that cleans and kills. It’s the sanitizer, only that it is now more powerful and in more quantity than before the shock was added.

Do You Need to Shock the Hot Tub After Each Use?

You should not shock the hot tub after each use because it will lead to a very high level of chlorine and low pH in the water. Hot tub water with a low pH and high chlorine level will damage the hot tub.

Shocking your hot tub should only be done when the chlorine levels are very low and when there is too much scum or bacteria in the water. It will take days after adding sanitizer to the water for the sanitizer to get depleted or used up to a point when you have to shock the water.

Chlorine for instance lasts in a hot tub between 3 days during very heavy use and 7 days during regular use. Heavy use here means constant use by a large number of people for days. That’s unlikely but let’s assume you decide to host a weekend party and it happens, you still wouldn’t need to shock the hot tub till after 3 or 4 days of consistent usage.

Bromine sanitizer which is a bit less potent than chlorine lasts longer in a hot tub. Bromine can last up to 8 days in a hot tub and still remain active. So take it easy on the hot tub shock.

Related Read>>> How To Shock a Salt Water Hot Tub?

What Chemicals Do I Add to My Hot Tub After Refilling?

You should add a sanitizer, either bromine or chlorine to the hot tub after refilling it. Then you should test for the properties of the water and adjust it as needed with the right chemicals.

What chemicals do you need to add to your water after re-filling? Chlorine, bromine, and many more.

After refilling your hot tub with fresh water, the first chemical to add is a hot tub sanitizer of your choice. You can pick chlorine, bromine, or any other alternative. The sanitizer will remove all impurities in the hot tub and keep the water clean for the first few days.

Chlorine is the most common hot tub sanitizer. Most hot tub users prefer to use chlorine as their sanitizer because it is more potent than any other sanitizer.

Chlorine is very effective in ridding your hot tub water of any contaminant, bacteria, or germs and it dissolves fast in the water. A major disadvantage of chlorine is the strong offensive odor of chloramines that it produces after usage.

Bromine is another popular choice for hot tub users that have very sensitive skin. Bromine is much gentler than chlorine but it is more expensive which is a disadvantage.

Other common choices of hot tub sanitizers include biguanide, minerals, UV (ultraviolet) light and some hot tubs use salt through the salt cell chlorinator.

Related Read>>>  Can You Use Chlorine Shock in a Bromine Spa?

What Else?

After adding the needed sanitizer, you should adjust the properties of the water by adding the needed chemicals to make the water ideal for soaking in. You should check the water pH level, calcium hardness level, total alkalinity, and iron levels in the water. If any of these is below or above the ideal level for a hot tub, you should adjust it with the needed chemicals. You can use hot tub test strips to test for all these.

The ideal pH level for a hot tub is between 7.2 and 7.8 on the pH scale with 7.5 being the sweet spot. If the pH level is high or low, you can correct it by adding pH decreaser or pH increaser to the water.

The total alkalinity level should be between 80ppm and 120ppm. If the total alkalinity is off, you should correct it.

The ideal calcium hardness level for a hot tub is between 80ppm and 220 ppm, with 180ppm being the sweet spot. If the calcium hardness level of your hot tub water is off, the water will start to foam.

Related Read>>> Things That Could be Affecting your pH Levels

How Long After You Shock a Hot Tub Can You Go in?

You can go into your hot tub after shocking it when you have tested the water and the chlorine level is below 3 parts per million (or 3 PPM) on your test strip. You can also use the hot tub after shocking it when the pH level of the water is below 7.8 on the pH scale.

After shocking your hot tub, the chlorine level can rise to 5PPM in the water. So it’s not right to get in your hot tub immediately after shocking. You should wait till the chlorine level is below 3PPM. This is the ideal chlorine levels for hot tubs.

Related Read >>> How Soon Can You Use a Hot Tub After Adding Chemicals?

How Often Should You Drain and Refill a Hot Tub?

You should drain, clean, and refill your hot tub every 3 or 4 months. Draining and refilling your hot tub should be done 3 or 4 times a year to get rid of the accumulated residue in the hot tub water.

Due to the presence of chemicals and sanitizers that you add to your hot tub water, the water in the hot tub can be used continuously for up to 4 months before you will need to change the water. The chemicals and sanitizers like bromine and chlorine that you add to the water keep the water clean, healthy, and safe by killing bacteria and scum that enter the hot tub.

However, these chemicals and sanitizers leave a little parting gift called used-up chemical (bromamines for bromine and chloramines for chlorine sanitizer).

The used-up chemical is chlorine or bromine that has been cleaned, disinfected, and mixed with hot tub scum hence, used chlorine. Every time the chlorine in your hot tub gets used, it leaves a little residue. So the more chlorine your hot tub uses, the more used-up chemical residue you will have in the hot tub till it gets to a stage where you need to drain the tub. This stage is after 3 months.

How to Figure Out When to Drain Your Hot Tub

As an expert tip, you can figure out when to drain your hot tub by testing the water regularly for TDS. When testing the water, you should test for the level of total dissolved solids (or TDS) in the water. TDS shows the level of all dissolved solid particles in the water. A high amount of TDS in the water shows you need to drain the water to get rid of the dissolved solids.

Having a hot tub with a high TDS reading can make the total alkalinity of the hot tub go off. So a high TDS level is an indicator that you need to drain your hot tub.

You need to drain the hot tub every 3 months to prevent an accumulation of used-up chemicals. An accumulation can raise the pH level, cause foaming in the water, cause staining on the hot tub shell, and can cause a nasty case of hot tub scale build-up.

Final Words

Overall, shocking your hot tub isn’t a practice to make a habit of. You only need to shock the hot tub whenever the sanitizer level is low or below the recommended level (1ppm for chlorine and 3ppm for bromine).

As a tip, always test the pH level of your hot tub before you add hot tub shock to the water so you don’t alter the pH levels.

Hi, I'm Calvin Hall, the owner of Hot Tub Wiki. I worked at a local Spa Service for a few years before creating this website. I have owned several hot tubs and fixed a thousand of them. So, I know a thing or two about hot tubs.