Can One Use Pool Shock in a Spa?

"Shocking" a pool or hot tub is a surefire way to clean the water quickly, or so most people with hot tubs or pools will tell you. And it is true, the approach will seem effective, but too much shocking can have serious repercussions for your hot tub enjoyment. So yes, you can use shock, but be aware of the risks involved.

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What is "Shocking"?

  • Shocking your spa is essentially using a significant amount of chlorine, more than is usually recommended for maintenance, to cleanse the tub water immediately. The amount is so great that all bacteria and algae in the water die.

Problems with the "Shock" Approach

  • Hot tubs and spas get dirty because they are not maintained frequently enough. There are two methods of cleaning, generally: chemicals and filters. The filter catches the larger contaminants such as dirt, leaves, and bugs before they get into the pump and recirculated via the jets. Chemicals keep the tub water balanced and kill off algae and bacteria. This combo effect in turn clears the water and removes odors from live algae and bacteria. First, using a shock approach means using far more chlorine than necessary to get a fast effect. The water will be so chlorinated your eyes will burn and it will be hard to breathe if you get in the water right away. Most product makers recommend the treated water be exposed to air for at least two hours before using the spa. Second, the core hot tub feature, the bubbles, aerate the chlorine in the water, which can poison a person quickly if he is sitting in the tub near the water line. This can result in a serious health risk, particularly in children and those with breathing problems. Chlorine can be just as poisonous to people as it is to bugs and algae.

The Chemical Reaction

  • When chlorine is put into pool or hot tub water, it combines with the material in the water. It will sanitize at first, but eventually it loses this sanitizing property, which in turn requires more chlorine. However, in the meantime as it bonds with contaminants, the chlorine changes into chloramines, which cause the chemical pool smell commonly picked up at public pools. To get away from this, actually more chlorine is needed to overcome the polluted material already in the water. Once done, then the water can be maintained at a safer sanitizing level. This is the correct use of "shock."

Lack of Measurement Causes Problems

  • Most people just throw chlorine into their hot tub and never measure the results. Thus, the maintenance level is usually never reached and what you get instead is chlorine combined with contaminants that causes a big chemical stink in the hot tub and skin irritation for users. Never reaching the optimum level, owners then are always chasing an elusive clear water level and suffering with the conditions of chloramines.

A Proper Superchlorination Level

  • Your superchlorination level for your hot tub -- the point when you overcome the contaminated chlorine and truly sanitize your tub - will be specific to your individual hot tub need. No general formula will work for everyone. Determine the appropriate dosage yourself from testing your water and measuring the right amount of chlorine added to do the job. Not enough and you get irritation, too much and the water won't be safe to use for a long time (days). A formula exists, but you must perform your own calculations for your specific tub size.


  • Photo Credit Image by, courtesy of Aaron Kohr
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