Spa Shock – How to Shock a Spa or Hot Tub

dr-pool-lightning-boltWelcome back spa and hot tub enthusiasts! We have a shocking topic for discussion today, How to Shock a Spa or Hot Tub.

The term “shock” is something of a misnomer, although you may envision the oxidation process as an electric shock, ripping through the water.

Shocking your spa effectively, for the right reasons, and without detrimental side effects, is the purpose of today’s lecture.

Don your lab coat and your protective eye wear, as we begin today’s chemical lab to better understand oxidation of hot tub contaminants.

What really happens when you shock a spa? Oxidation is the process of a particle losing electrons when it encounters a disinfectant.

oxidation-2In the case of granular chlorine, or non-chlorine oxidizer – spa shocks, the oxidizer rapidly steals the outer electrons of contaminants it comes in contact with. The loss of these electrons makes a contaminant vulnerable to attack at a cellular level, which quickly destroys the molecule.

Reasons for Shocking a Spa or Hot Tub

fourThere are only four valid reasons for shocking your spa or hot tub. It’s not necessary to shock the spa every time you use it, and maybe not even weekly. Shock your spa for these four reasons:

  1. To remove bromamines or chloramines in the spa. Using a DPD test kit, you can test for the level of combined chlorine or bromine. Adding an oxidizer in the amount equal to 10x the level of combined sanitizer will break apart these bonds.
  2. To remove organic contaminants in the spa. When 3 or 4 users jump into a hot spa, the level of contaminants spikes to a level many times higher than your sanitizer can manage. Adding an oxidizer afterwards will restore sanitary spa water.
  3. To reactivate bromides in your spa water. For a bromine spa, using an oxidizer weekly helps to maintain a consistent bromine bank in your spa water. Activating bromine ions with spa shock converts them to hypobromous acid, the killing form of bromine.
  4. To Kill bacteria. Remember that non-chlorine shock is not classified as a disinfectant, like chlorine or bromine, but is useful only as an oxidizer. Use chlorine spa shock to kill all bacteria and pathogens.

Preparing to Shock a Spa or Hot Tub

The most important thing to do in preparation for shocking the spa water is to first test the spa, and adjust the pH to the range of 7.2-7.6. Oxidizers work best in a low pH environment, and the efficacy of your spa shock is twice as great at a pH of 7.6, than it is at a pH of 8.0.

spa-cover-removal-before-shockingThe second most important thing to remove your spa cover, spa blanket and spa users – before shocking the hot tub. Especially during the first 20 minutes, your spa surface needs to be aerated, to facilitate the exchange of electrons, and gassing off of byproducts formed during oxidation.

The third most important thing is calm water – don’t turn on the blower, but do run the circulation pump when you shock the spa – too much agitation can prematurely gas off potent oxidants.

Shocking a Spa or Hot Tub

When shocking the spa, for the above reasons only – pay attention to a few things. Specifically, be cautious when using spa shock, oxidizers can be dangerous when misused or mishandled.

  1. Read the Label – different oxidizers have varying strengths – be careful not to overdose or underdose your spa shock treatment.
  2. Measure your spa shock – dosing is so important, if you are 1/2 of an ounce off, you can underdose or overdose your spa.
  3. Add Carefully – high winds can blow spa shock right in your face. Gently pour it over the surface, and wash away any spills right away. Keep out of the reach of

Which spa shock should you use? Use an oxidizer specifically labeled for use with spas and hot tubs. Don’t use bagged pool shock in your spa.

We have a large variety of spa shock that can be used for oxidation. Choose one you like and get on with it!

Remember my cautions above when using spa shock, because – Oxidants Happen! Sorry, couldn’t resist…


Dr. Pool


Spa Shock – How to Shock a Spa or Hot Tub — 14 Comments

  1. We have just cleaned and refilled the spa, I have used the spa shock granules as measured and am running the spa on low
    Why do the granules just sit on the bottom or will they disintegrate?

    • Hi Jay, generally speaking, most MPS (non-chlorine) spa shock will dissolve instantly. Chlorine shock will take longer to dissolve completely, and can be pre-dissolved into a clean bucket or pitcher of water, and then added (always add shock to water, not water to shock). Also, spa shock that has been exposed to moisture may take longer to dissolve, and may have lost some of it’s power. For granules that sit on the bottom, in most cases they won’t harm the surface, but to reduce the risk, use a brush or net to stir them around.