Do you really need to shock your spa every week or so?

wayner

LifeTime Supporter
May 31, 2012
602
Toronto, ON
Pool Size
100000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Jandy Aquapure 1400
I was told to do this when I first got my spa - that was about 14 years ago. Since then I have reduced the frequency of the shocks without any ill effects. Not as an explicit strategy but out of laziness. Since I went to a drop-in SWCG two years ago my spa it is clearer than ever. My spa isn't used a lot - probably 1-2 bathers per week (usually me).

Do you really need to shock a spa every week or so?

FYI - My spa is a Jacuzzi and is standalone. It is always covered when not in use with a ~4-6" thick foam cover.
 

dan1333

Active member
Nov 1, 2020
25
Orange, CA
I never shock my hot tub. I just maintain the free chlorine with bleach additions after use and then my drop in swcg maintains the free chlorine the days I don't use it. So far I have crystal clear perfect water and it's been almost 5 months.
 

RDspaguy

In The Industry
Mar 21, 2020
1,290
Cabool, Mo
Frequent shocking is recommended to counter the high CC (or bromides) created by such heavy bather load (gallons per person). A SWG burns off CC in the generation process, or so I have heard, which lowers or eliminates the need to shock. Ozone and UV have a similar effect, but also oxidize FC. The once a week thing is a rule of thumb that goes back to when everyone used bromine in a spa. I recommend more frequent shocking when using just chlorine. Your actual chemical needs can only be found with a good test kit.
 
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wayner

LifeTime Supporter
May 31, 2012
602
Toronto, ON
Pool Size
100000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Jandy Aquapure 1400
I do test every few days with my FAS-DPD test and I am generally around 3-4 FC and 0 CC. My water also seems much clearer with less foaming since I switched from bromine to SWCG. I rarely have trouble with FC but I am in a constant see-saw between pH and TA as my pH gets high, so I add MA, but then my TA gets down to 20 or 30, so I add Baking Soda, but then my pH goes up so ...
 

cranbiz

Active member
Feb 17, 2021
30
Wentworth, NC
I'm still on the @ease system simply because my dealer included a years worth of chemicals with my purchase. They recommend shocking once a week and that's what I do.

So far, everything has tested just fine and we use the spa at least 5 times a week for 20-40 minutes 1-3 bathers.
 

RDspaguy

In The Industry
Mar 21, 2020
1,290
Cabool, Mo
Sounds like it's doing well for you.
Get your ph were it needs to be and let the alk land where it will. Once it's stable post ph, alk, and calcium hardness.
Do you use borate? Many folks like it for ph stabilization, though I have never used it myself.
 
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RDspaguy

In The Industry
Mar 21, 2020
1,290
Cabool, Mo
Also, aeration raises ph, so keep all air control valves closed when not in use. Your swg is going to raise ph as well in my experience, and high ph is bad for the cell.
 
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wayner

LifeTime Supporter
May 31, 2012
602
Toronto, ON
Pool Size
100000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Jandy Aquapure 1400
I do get the pH back down but it keeps going up. I keep the aeration valves open, so I will close them and only open when in use.
The other thing that is weird is that I have to use a lot more MA than what the Pool Math app says. For example - when I have a pH reading of 8.2 it will say to add something like 13mL to bring the pH down. If I had that amount it will do very little to bring the pH down. And I am pretty sure that I have the right volume for my spa.
 

5tan

Active member
Jan 9, 2021
37
Canada
Pool Size
1643
Chlorine
Liquid Chlorine
Using 10.3% pool chlorine, I shock weekly and also after heavy usage, by using the breakpoint chlorination method described below, raising to 10ppm FC and continuing to add more chlorine every few hours until the FC starts to holds steady at 10ppm.

Shocks are used to get rid of 2 types of chloramines: inorganically bound, and organically bound. "Breakpoint (#3 below) is an efficient way to deal with inorganically bound chloramines. However, it is not very effective at removing the organic bound types. Proactive methods of oxidation, such as regular super-chlorination using unstabilized chlorine (#1 below) or the addition of ozone and/or UV, can help prevent formation of the organic bound chloramines."

According to You are being redirected..., there are three types of "shocks", each with specific processes and usages depending on situation:
1) Super-chlorination: increasing the level of chlorine to sufficiently sanitize a pool, clear hazy water and deal with limited algae growth. When superchlorinating, chlorine is added to raise the measured free chlorine level to 10 to 20 ppm.

2) Hyper-chlorination: used in situations when a pool needs to be completely disinfected, in which the chlorine level is raised to 20 to 40 ppm. One such situation would be a case of suspected contamination from a chlorine-resistant germ. For example, cryptosporidium is commonly spread in pools after an accidental fecal release.

3) Breakpoint chlorination: used specifically for the purpose of breaking apart and removing combined chlorine or chloramines. Breakpoint chlorination is NOT used to clear green pools or deal with crypto. In the pool industry, historically (and incorrectly), the breakpoint ratio of chlorine to chloramine is 10 to 1. However, this old breakpoint calculation was faulty math based on the contaminants being 100% ammonia, and did not factor in chlorine binding to urea, creatinine, and other organic compounds.

You will often see the pool industry use this 10x rule of thumb, stating to add 10ppm chlorine (FC) per 1ppm Combined Chlorine (CC), and this is completely wrong and results in over-chlorination.

The correct math (per below source) says that if the compound to break apart contains ammonia, then you need 0.5x FC to CC. If the compound is urea, then 3x at most. The proper real world method to achieve breakpoint chlorination is to "keep adding chlorine until the FC starts to hold, though it may be in two phases -- first where the chlorine is consumed very quickly (in less than a minute) as it converts ammonia to monochloramine -- then a slower second phase that takes hours where it converts monochloramine to nitrogen gas (about 4 hours if CYA is in the water) or oxidizes partially degraded CYA."

Richard Falk's (chem geek) writings about breakpoint chlorination:
There is a molar relationship of 3:2 for chlorine to ammonia. Chlorine is measured in ppm Cl2 units, where molecular chlorine has a molecular weight of 70.906 g/mole. Ammonia is measured in ppm N units, where atomic nitrogen has a molecular weight of 14.0067. Therefore, in terms of a chlorine to ammonia ppm (weight) ratio, it is (3*70.906)/(2*14.0067) = 7.593. In practice, due to side reactions producing nitrate, the actual weight ratio needed for chlorine oxidation of ammonia is 8 to 10. This is where the 10x pool industry rule-of-thumb comes from.

Now let's look at how this very valid rule was misapplied in the pool industry. The pool industry took this rule and applied it against Combined Chlorine (CC). The first major flaw is that CC is measured in molecular chlorine units (i.e. ppm Cl2), NOT ammonia nitrogen units (i.e. ppm Nitrogen). So there is no factor of 70.906/14.0067 = 5.062 weight difference. The second major flaw is that CC already has chlorine combined with ammonia - presuming it is mostly monochloramine, which should be the case if one starts with ammonia. So 2 of the 3 initial chlorine would have already been used up combining with the 2 ammonia. The molar ratio of what is left is only 1:2, not the original 3:2. In practice, it would take a little more than this 0.5x amount, but the point is that it is nowhere near the presumed 10x rule.

Even if one goes through this same analysis using chlorination of urea (instead of ammonia), one doesn't get to more than 3x at the most. The 10x rule is completely wrong in its application to CC because (1) the unit of measurement of CC is 5 times larger than that of ammonia so takes 1/5th as much chlorine compared to ammonia and (2) chlorine is already part of CC so it takes less chlorine to further oxidize it.

The pool industry got it wrong decades ago and everyone has been following the 8x to 10x rule like lemmings ever since (again, the rule IS correct against ammonia in ppm Nitrogen units). The breakpoint chlorination "10x" rule only applies to the ammonia measured in its own units of measurement (ppm Nitrogen).

The largest nitrogenous component of bather waste is urea, not ammonia, so the biggest problem with CC in higher bather-load pools is mostly due to a buildup of urea in the water. Chlorine combines with urea rather slowly so urea concentrations can build up at which point the intermediate CC (monochlorourea) can show up. If you have a lot of built up urea and try to raise the FC level to get rid of the CC, the CC level may rise instead of fall. Increasing FC can have the CC decrease IF the chemical to be oxidized is ammonia, but the CC can INCREASE if the chemical to be oxidized is urea, because urea is much slower to combine with chlorine.

In spas, most of the chlorine is used to oxidize bather waste. In between soaks, however, the chlorine level is kept lower, but right after a soak a lot of chlorine is added to oxidize the bather waste. This is where an ozonator can help cut that chlorine usage roughly in half if the spa is used every day or two. Unfortunately, ozone also reacts with chlorine, so in between soaks, if the spa isn't used frequently, the chlorine demand is at least doubled due to the ozone. The ideal situation would have the ozonator turn on right after one ends one's soak and stays on for 12-24 hours depending on how long it takes to oxidize the bather waste. The ozonator would then turn off until after the next soak. That way chlorine can be kept at a low 1-2 ppm FC level with 30-40 ppm CYA the entire time so provides for disinfection in the background but is not the primary chemical used for oxidation of bather waste.
Source: Breakpoint Chlorination

Also note that CYA has a strong blunting effect on chlorine shocks:

"Pools with high levels of CYA would require much more chlorine to achieve breakpoint based on the binding of CYA to HOCl. There are current studies stating that for chlorine to be effective in the presence of CYA, there must be a ratio of 20 to 1. In the presence of high CYA, chlorine will not be as effective and that includes when using breakpoint. It is because of this that tri-chlor and di-chlor forms of shock should not be used when attempting breakpoint chlorination."

Since organic chloramines are not effectively broken up by breakpoint shocking, "proactive methods of oxidation" must be taken to prevent the formation of organic chloramines. Such proactive oxidation methods are: superchlorination, ozone, UV, and potassium monopersulfate (aka MPS, KMPS, non-chlorine shock, etc.)

However, it should be noted that potassium monopersulfate aka MPS and/or trace amounts of compounds in MPS products are well-documented in dermatology literature to cause severe contact dermatitis in some people. Anyone experiencing chemical burn type itching or unexplained hot tub itch should discontinue MPS usage. Note that products like weekly pre-dosed packets like the SoftSoak Trio kit contains MPS not indicated on packaging but indicated in MSDS.

When doing any of these 3 shocks, it's a very good idea to open the spa cover, circulate the water for 30 minutes, and allow the area to thoroughly air out, in order to dissipate any disinfection byproducts (DBPs). DBPs are likely to have harmful and carcinogenic effects to humans.
 

wayner

LifeTime Supporter
May 31, 2012
602
Toronto, ON
Pool Size
100000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Jandy Aquapure 1400
Using 10.3% pool chlorine, I shock weekly and also after heavy usage, by using the breakpoint chlorination method described below, raising to 10ppm FC and continuing to add more chlorine every few hours until the FC starts to holds steady at 10ppm.
This seems like a lot of work, and expensive since FAS-DPD powder is more expensive than cocaine in Canada (not that I am aware of the current price of cocaine), and FAS-DPD tests would be required to test at a 10 ppm level. How many tests do you do and how many hours do you keep this up for?

What is the necessity to do a breakpoint chlorination if your CC is always 0 or below 0.5? And I ask that question for both my pool and spa? How long after a shock would it take for a spa to then get down to "normal" levels of under 5?

Other than when opening the pool in May, my pool is never shocked and it is crystal clear and the CC never gets to 1.

How do I know what is in my "Spa Shock"? I use Lawrason's Spa Life Shock. The label doesn't say what it contains. Does this contain MPS? Lawrason's, Inc. Pool and Spa Products - SPA LIFE Shock

I do get occasional itchiness after using the spa, but it isn't that bad and I didn't know if that could be caused by other issues, like a high pH or temporarily high FC.
 

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5tan

Active member
Jan 9, 2021
37
Canada
Pool Size
1643
Chlorine
Liquid Chlorine
I use the SenSafe DPD-1 reagent strips that are $14USD for 100 tests - it's a 10 second test. Following heavy usage, I bring pH down to the 7.0-7.6 level, then add Canadian Tire's Aquarius Pool Chlorine with both pumps on, using the PoolMath/PoolCalculator amount for reaching the 10ppm FC level based on the current FC level (superchlorinate), then recheck after a few hours, and repeat until the spa stays at the 10-12ppm level ~6 hours later (breakpoint achieved). I have the chlorine amounts needed pretty much memorized for any given FC level, so none of this is a lot of work, about 5 minutes from opening the spa cover to closing it and putting my test kit away.

If there is light to zero usage after the last breakpoint shock, I don't need to test the water or add chlorine for up to a week.

When doing a shock, I disable the ozonator by turning off both heater and filtration (I have a continuous circulation pump that handles filtration, separate from the other 2 pumps). If either heat or filtration runs, it turns on my ozonator, which causes chlorine demand to be significant, losing 50% or more every 24 hours depending on the duration of the heating or filtration cycle.

For me, it is easy to get FC down from 10 to normal levels (3-6ppm) by running filtration or by heating the water, either will enable the ozonator. For those without a powerful ozonator, you can do a few things to lower FC: open your cover and let nature and sunlight fall into the water, run the jets on high to aerate, and/or neutralize the chlorine with hydrogen peroxide.

If your CC test is good and your water truly has a CC=0.00, and your water doesn't have a smell of chlorine (which is usually actually the smell of chloramines), then you don't have any chloramines to destroy using a breakpoint chlorination, so you don't need to follow the breakpoint procedure. Sounds like your regime is working for you!

From the Spa Life Shock MSDS, it is 80-100% Potassium peroxymonosulfate (K5H3(SO3(O2))2(SO4)2), CAS # 70693-62-8. Your usage of non-chlorine shock is a proactive oxidation method to prevent the formation of organically-bound chloramines.

I don't use any non-chlorine shocks whatsoever, as I don't want my guests to have contact dermatitis after. You never know who's allergic to what, and more people are allergic to MPS than pool chemical specialists and non-dermatologists know about. Since I don't use MPS, I superchlorinate after heavy use, then continue to add chlorine to reach breakpoint, identified when the rate of FC decline tapers off. My regime works for me, been doing it for many months now.
 

wayner

LifeTime Supporter
May 31, 2012
602
Toronto, ON
Pool Size
100000
Surface
Vinyl
Chlorine
Salt Water Generator
SWG Type
Jandy Aquapure 1400
Regarding my CC, when I add the 5 drops of the R-003 reagent the samples will often turn just the slighted shade of pink. This will then be neutralized by 1 drop of the 871 liquid. So this would indicate a CC of 0.2 or lower if using a 25mL sample, or less than 0.5 using a 10mL sample.

If I wanted to use chlorine rather than spa shock I guess I need to figure out how much liquid chlorine to add to get to a FC of 10. I have no CYA in my spa so that isn't an issue. After getting up to an FC of 10 how long does it take to get FC back down to a more normal level below 5 or so?