Spa Shock – How to Shock a Spa or Hot Tub
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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 children.spa-shock-oxidizers-for-hot-tubs

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…

DrPool-thumb

Dr. Pool


Comments

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.

    • Hi Mo, not before draining, unless you have a spa that has turned green or become stagnant. And not after filling, unless you suspect that the fill water may be unsanitary – which could happen. Shocking the spa is done for these reasons 1). To kill invisible bacteria and other pathogens that escape normal daily sanitation, and 2). To kill visible algae, mold or bio-film on surfaces, and 3). To break down contaminants like soaps, lotions, hair products, and 4). To remove combined chlorine (chloramines) and combined bromine (Bromamines), and 5). To reactivate bromide ions into active free bromine.

      Generally, most spa owners shock the spa every week or two, usually after exiting the spa. Follow label instructions, always use spa shock (not pool shock), and leave the cover off the spa for 30-60 mins afterwards. A good pH level of 7.2-7.6 is helpful to allow the shock to be most powerful.

    • Hi Ryan….generally my hot tub is not in use from Monday till Thursday, can I give it a shock on the Thursday morning and how long after shock can it be used?
      I have a 1500 Ltr tub, what measure of shock should I use?
      Will the shock raise the bromine level???
      Thanks for your help Ryan.

      • Hi, how much shock you should use in a spa, depends on the purpose of the shock, and what type of shock you are using, and of course how much water is in the spa. It also matters how much the spa is used 1-2x per week, or 3-4x per week – because the more it’s used, and the more people that use it, the more contaminants (from us!) that the shock needs to oxidize. For just 1-2 people, once or twice per week, the contaminants should not be out of control, so a normal dosage can be used, once per week. Assuming that you don’t notice any adverse water conditions (smell, color, cloudy, algae, foam), a normal dosage is also indicated. For spas with many people using it, or with noticeable water problems, or if power was shut off for a few days or for pump/filter repairs – then you can increase the dosage of spa shock, up to double or triple the amount shown on the label. For heavy use spas, once weekly shocking may not be enough, some spas need it almost daily. Good filtration and water balance is also important, and can affect the amount and frequency of spa shock needed.

        For your spa, since you don’t it that much, a weekly shock is fine (assuming that your filtering all week long, and maintaining a bromine level). Non-chlorine shock may state that you can use the spa immediately after treatment, but I’d wait 20 minutes, to let it do its thing without introducing more contaminants (you!).

        Adding shock to a bromine spa will increase the bromine level, yes. That is, if you have a good ‘bromine bank’, or build-up of bromide ions in the water. Aside from bacteria and bromamine removal, one of spa shock’s main roles in re-activation of bromide into bromine. When shocking a spa, some of the shock is destroying contaminants, and some is boosting the bromine level, and a heavy shock can raise your bromine level very high for awhile.

        For your 1500L (400 gal) hot tub, consult your dosage on the label, but it’s probably 3-4 tablespoons, or 1-2 ounces (28-57 gm) per treatment. Your own experience is a good tool to use, knowing the spa, and how it responds to certain dosages (given good water conditions and water balance), and will help guide your hand in treatment.

  2. How long should you wait after the shock treatment? If the water is very cloudy, Is it bad to do both a non-chorine shock, wait, and then do a chlorine shock? How long should I wait in between ?

    Thanks,
    Eric

    • Hi, you could use both, but i would probably wait about an hour between adding. Just be careful not to overdose, on either types of shock. Keep the cover open after shocking, and be sure not to mix oxidizers (or other pool chemicals)…

    • Hi, I like to use poolcalculator.com for such questions. You can type in gallons at the top, then set your current and target FC (Free Chlorine levels), then select your shock type from the drop down menu and… in your case, if you wanted to shock it good, to 10 ppm, you could use 0.5oz of DiChlor shock, or 0.4oz of Cal Hypo 65% available shock. If using non-chlorine shock, also about 1/2 oz.

      However, always consult the label on the bottle for specific treatment and dosage guidelines. Your pH levels should be proper for best shock effect. When shocking a spa, turn on the jet pump, and leave the covers off, to allow chlorine to gas off (and not harm your spa cover). Wait to use the spa until chlorine drops below 5 ppm. If using non-chlorine MPS shock, you can recover it or use it almost immediately.

    • I have a great formula for you – for 400 gallons, add 0.1 oz for every 1.0 ppm of chlorine you want. As you can see it’s very little. If you just want a little 1 ppm boost, add a teaspoon, or 1/10 of an ounce. Add a tablespoon full for a 4ppm superchlorination or 2-3 tablespoons for poor water conditions or algae. It doesn’t take much, use very little! By the way, we don’t recommend using pool shock for spas. Spa shock is much finer, suited for hot water, labeled correctly…The larger problem is that opened 1 lb bags of pool shock can be dangerous, the can spill, become contaminated or become wet – from open/closing the bag repeatedly, like you would for a spa.

    • Hi Mary Anne, the reason we don’t recommend bagged shock for spas is because storing opened bags of shock can be hazardous, from spills, moisture and humidity or contamination. It also tends to be slow dissolving, or not as fast as shock made specifically for spas. Also, granular chlorine should not be used in containers or with scoops that have contacted other chemicals. The smallest amount of residue is enough to cause a reaction, including explosions and fire.

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