Misplaced Spa Calculations For Reducing Chlorine Using Hydrogen Peroxide

bxcrwlly

LifeTime Supporter
Dec 3, 2012
123
Central Florida
I seemed to have misplaced my once received from the forum, guidelines on how much Hydrogen Peroxide to use in my spa to reduce chlorine to a tolerable level around 3-5ppm. I did a bit of online research and found a few articles one of which talks about 2 ounces Hydrogen Peroxide for every 100 gallons of water and have also seen reference to a 1-1 ratio of Hydrogen Peroxide to PPM Chlorine. My spa is a round in ground unit and contains 243 gallons of water.

Any feedback from the forum is greatly appreciated. If I'm recalling correctly, it may have been ChemGeek who gave me an original formula, but just not sure.
 

ajw22

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TFP Guide
Jul 21, 2013
11,633
Northern NJ


 
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jimbethesda

Gold Supporter
Jul 2, 2018
267
Austin, TX
I seemed to have misplaced my once received from the forum, guidelines on how much Hydrogen Peroxide to use in my spa to reduce chlorine to a tolerable level around 3-5ppm. I did a bit of online research and found a few articles one of which talks about 2 ounces Hydrogen Peroxide for every 100 gallons of water and have also seen reference to a 1-1 ratio of Hydrogen Peroxide to PPM Chlorine. My spa is a round in ground unit and contains 243 gallons of water.

Any feedback from the forum is greatly appreciated. If I'm recalling correctly, it may have been ChemGeek who gave me an original formula, but just not sure.
What‘s your CYA level? As long as your chlorine is at or below shock level for your CYA, no need to reduce it. Is your chlorine the same level in your pool?
 

bxcrwlly

LifeTime Supporter
Dec 3, 2012
123
Central Florida
jimbethesda.....jim. Haven't checked CYA in a while....shame on me. Usually try to keep CYA between 70 & 80ppm. Chlorine in pool is/has been definitely below shock level. Came in as of 12/7/19 at 5ppm. I should've mentioned my spa has an overflow(spillover) to the pool which is on on at all times except when I'm in the spa, so the chlorine level in the spa would be the same as the pool except when spa is isolated. That's when the chlorine concentration jumps up because I'm dealing with 243 gallons of water isolated vs. 11,600 gallons when the pool and span are circulating.
 

ajw22

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TFP Guide
Jul 21, 2013
11,633
Northern NJ
Your ET should be able to reduce your IC20 % output when in SPA mode to not over chlorinate the smaller body of water.

How long fo you run the Spa? If the FC level in the spa starts the same as in the pool it should take a while for the spa FC to get excessive from the IC20 generation.

Can you put some numbers around the problem you are trying to solve?
 

bxcrwlly

LifeTime Supporter
Dec 3, 2012
123
Central Florida
IC20 reduces chlorine to isolated spa to 2%. Trying to solve when switching circulation from pool & spa to isolating spa, a formula to know how much hydrogen peroxide I need to add to spa. Spa is 243 gallons. Say as an example chlorine is 10ppm when I initially isolate. I’d want to reduce from 10 to at least 5ppm before getting in. I had a factor at one time that I could use to know that info. Trying to recreate formula.
 

YippeeSkippy

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Jan 17, 2012
11,989
Evans, Georgia
For some reason I recall using 1 ounce of Hydrogen Peroxide per 1ppm FC to reduce. I did this many years ago so I may be off, but this rings a bell to me. So like you want to reduce your FC from 5ppm to 3ppm, try 2 ounces of peroxide.

Or maybe it was 2 ounces for each ppm of FC???

Darn... it was a fairly simple method. Let us know if you try that and it works.

Maddie :flower:
 

AUSpool

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Sep 23, 2015
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I used hydrogen peroxide a few years back Here.

Going straight to the juicy bits, I found in practice that 68 fluid ounces of 19% H2O2 in 10,000 gallons would lower FC by 10ppm or in metric it’s 530ml of 19% H2O2 in 10,000L to lower FC by 10ppm.

And this from JofulNoise;
The quick and dirty rule of thumb is this - the amount in oz of 6% bleach it takes to raise your FC by X ppm's is equal to the amount of 3% H2O2 needed to lower the FC by X ppm's. That rule of thumb is good to use because it's a lot easier to find 3% peroxide in a drug store and most people use peroxide as an FC lowering chemical in spas where the water volumes are A LOT lower.
 
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mrwoo

Well-known member
Nov 9, 2019
54
kalispell, mt
What‘s your CYA level? As long as your chlorine is at or below shock level for your CYA, no need to reduce it. Is your chlorine the same level in your pool?
I have a question (well, a few). Are you saying that if I had 40ppm CYA, that if my FC is below the "SLAM" value on the Chlorine/CYA chart (which is 16) it would be fine to use the spa? Or, do you mean the shock value as in 10x FC to the amount of CC, which I think is how you figure out how much chlorine to use to shock. I did not think shock and SLAM were the same, but they might be.

Also, relating to this thread, I have purchased some 100% Sodium Thiosulfate Pentahydrate that is crystalline and requires 1/4 tsp per 1 ppm FC to drop. I like the idea of hydrogen peroxide as well. Is there a disadvantage to either, where for the overall welfare of the water off-gassing over time would be more beneficial? The thiosulfate works really well and really fast.

Thanks.
 

mknauss

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May 3, 2014
22,960
Laughlin, NV
Shock is poor term. It is a product, not an action.
The SLAM Process is an action.

And yes, you can use the spa with a FC level up to the SLAM FC level based on your CYA. There is no reason to ever use a FC reducer. It will drop on its own very quickly in most situations.
 

jimbethesda

Gold Supporter
Jul 2, 2018
267
Austin, TX
I did not think shock and SLAM were the same, but they might be.
SLAM is an acronym..should really be S.L.A.M. It stands for Shock Level And Maintain. If you need to SLAM, you bring your water up to Shock Level (40% of your CYA as shown on that chart). And then Maintain that level until you meet all of the requirements to end it.

And yes, as Marty says, you can can safely swim/spa at FC up to 40% of your CYA (shock level).
 

mrwoo

Well-known member
Nov 9, 2019
54
kalispell, mt
Ok, but, are there 2 shock terminologies then? One is a product shock, such as mps. The other is a value aka "shock level".
40% of cya, easy enough to calculate. SLAM as a process yes I understand that you have to keep it there and check it etc. But isn't there a rule or whatever you would call it that says if you have CC of 2, then you would need 10x that in FC to "shock" it, which means 20+ FC? I thought I read something chem geek posted about that and that if you don't get over the 10x amount it can create more chloramines?

Sorry for being complicated, but there's a Crud ton of information here and sometimes hard to condense it down lol.
 

jseyfert3

Bronze Supporter
Oct 20, 2017
474
South-Central WI
But isn't there a rule or whatever you would call it that says if you have CC of 2, then you would need 10x that in FC to "shock" it, which means 20+ FC? I thought I read something chem geek posted about that and that if you don't get over the 10x amount it can create more chloramines?
Yes and no. According to the Taylor kit booklet I have, to completely remove CC you need 10x that amount of FC. However, we don't even mention this to users here on TFP, because they'd get confused, just like you are. :)

Now, why doesn't TFP tell this 10x rule to new people? Because there's no need to do so. If your CC level is so high you need to shock, then you should be doing a SLAM and not a one time addition of chlorine. Again, SLAM stands for Shock Level And Maintain. The key point there is maintain. You hold the FC level at the "shock level" until you can pass the OCLT, your water is clear, and your CC is 0.5 or less.

This is better on a number of levels for the average user. First off, it's less confusing. It's faster for getting the spa/pool back to usable, since you actively test and keep adding FC multiple times a day. It's nessissary, in the case of algea, as a one time addition of FC will almost certainly not kill the algea and so it's critical to quickly obtain and keep a high FC level. Finally, adding 10x the CC level doesn't consider the FC needed to maintain a typical pool, or again in the case of algea, the FC lost due to killing the algea.

Does this make sense?

As a postscript, I'd like to add that the SLAM is TFP specific, and unfortunately so. It's a good way of doing things. The "typical" pool industry advise is to regularily "shock" your pool/spa on a weekly schedule or similar, TPF does not recommend you regularly "shock" your pool/spa unless something indicates you need to. And if you properly follow TFP advise, you should never have to SLAM/shock, because regular testing and maintaining FC at the proper level in relation to your CYA should keep everything in check. Numerous users have reported crystal clear water year round in their pools, never "shocking" their pool, with zero algea, which is not typical for the non-TFP pool user. In other words, any "shock" or SLAM is almost certainly because you slacked off in pool care or testing. It is not, or should not be, a normal part of owning a pool/spa.
 
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mrwoo

Well-known member
Nov 9, 2019
54
kalispell, mt
Yes, it all does make sense and overall I thought I understood it. However, there is a lot of terminology thrown around that sometimes seems ambiguous. I read a lot here before I even had my tub installed, and followed what I thought would be a proven methodology. It would have been had I seen the note about calcium stearates and using Ahh-some to treat it.

My first two weeks were spent using dichlor and then bleach to play with how it worked. Then I started my swcg and it did not perform as I was expecting. So more reading, more questions. Simply because I want to know what to expect rather than react to the unexpected. In this process I have become perhaps a bit more confused because I am delving into deeper waters (pun intended). But that's okay, because I can absorb this data and will make use of it.

It's worth stating that I read the SLAM material and followed it but my CC's are always between 1.5 and 2. Before discovering the stearate issue I was scouring the webs for why it was not working.

So, my questions are a bit skewed because what I read wasn't working real life and then I went on an information tear and overloaded my poor little head.... but that's how you fill it up too ;)

Thanks yet again to everyone who takes precious time to help others understand.
 
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jseyfert3

Bronze Supporter
Oct 20, 2017
474
South-Central WI
However, there is a lot of terminology thrown around that sometimes seems ambiguous.
I suppose that can't be helped, when you have an open forum with 200k+ members. Don't worry, I get why you're asking questions. I love to learn about things as well, and spent untold hours reading lots of posts here and elsewhere on the internet when I first found this place.

I've actually thought the "How to use chlorine in a spa" sticky is a bit outdated. It was written in 2008 after all. Key points I think are outdated are things like no mention of CSI and instead genaric "ranges" of CH/TA, the recommendation to use MPS every week (not really a TFP recommended thing to add MPS once a week, plus it screws with your CC test unless you buy a regeant to remove the MPS), saying to shock to 12 ppm FC once a week, and the implied recommendation to use dry acid, which TFP generally recommends you avoid unless you have a compelling reason not to use muriatic acid. Also the lack of mention of cleaning new or used spas with Ahh-some or similar, etc. I've considered trying to write up a potential update to replace it, or at least kickstarting that effort. Maybe I'll do that after I get a "real" spa and get a bit more experience since we'll be using it year round vs the sometimes sporadic usage of our inflatable spa currently.
 

jimbethesda

Gold Supporter
Jul 2, 2018
267
Austin, TX
I would ignore all product names, and just look at the ingredients. “Shock” usually means it has chlorine as one of the ingredients in it, but not always.

If it doesn’t list the ingredients, run away.
 

JoyfulNoise

TFP Expert
Platinum Supporter
May 23, 2015
16,097
Tucson, AZ
The “10X Rule” refers to the industry labeled concept of “breakpoint chlorination” and, like many things the industry pushes, it is wrong. User @chem geek has posted the detailed calculations about this concept and, in order for chlorine to oxidize monochloramine, one only needs, at most, a 3X value. The problem is the industry doesn’t get the units of the calculations correct and so they overstate the amount of FC needed greatly.

See this wiki entry on @chem geek ‘s review and critique of standard CPO training materials.
 

ajw22

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TFP Guide
Jul 21, 2013
11,633
Northern NJ
I've actually thought the "How to use chlorine in a spa" sticky is a bit outdated.
TFP's focuis in on pool care. Many of the general principals apply but there are many differences in the nature of a spa/hot tub to generally apply TFP methods to them.

Key points I think are outdated are things like no mention of CSI and instead genaric "ranges" of CH/TA,
CSI only applies to plaster pools. Hot tubs/spas are generally fiberglass. Also, there is the assumption that spa/hot tub water gets replaced every few months. CSI is not a factor for stand alone spas/hot tubs.

the recommendation to use MPS every week (not really a TFP recommended thing to add MPS once a week, plus it screws with your CC test unless you buy a regeant to remove the MPS),
The assumption is spas/hot tubs are covered and you need some way to burn out the natural CCs that accumulate from its usage. MPS is a way to do that.

saying to shock to 12 ppm FC once a week,
Spas/hot tubs get a lot of use for the water volume and this ensures the water stays sanitary.

and the implied recommendation to use dry acid, which TFP generally recommends you avoid unless you have a compelling reason not to use muriatic acid.
Dry acid is not recommended for pools due to the buildup in sulfates. Sulfates can damage SWG's, plaster and concrete. You don't have these issues in a fiberglass standalone spa/hot tub that replaces water every few months. So dry acid can be used in hot tub/spas and some folks find it easier handling and safely storing dry acid.

Also the lack of mention of cleaning new or used spas with Ahh-some or similar, etc.
It is mentioned in the wiki -


I've considered trying to write up a potential update to replace it, or at least kickstarting that effort. Maybe I'll do that after I get a "real" spa and get a bit more experience since we'll be using it year round vs the sometimes sporadic usage of our inflatable spa currently.
Write up your techniques and let's see how it works. There are many ways to keep a spa/hot tub sanitary and safe.
 
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jseyfert3

Bronze Supporter
Oct 20, 2017
474
South-Central WI
CSI only applies to plaster pools. Hot tubs/spas are generally fiberglass. Also, there is the assumption that spa/hot tub water gets replaced every few months. CSI is not a factor for stand alone spas/hot tubs.
I was thinking if you happened to get a positive CSI you'd start scaling, but after playing with poolmath I realized you'd likely need a fill CH of like 500+ for this to really start being a concern, since your TA will almost certainly have to always be right around 50.

The assumption is spas/hot tubs are covered and you need some way to burn out the natural CCs that accumulate from its usage. MPS is a way to do that.
I suppose this depends on the usage. I haven't seen an issue with CC buildup with our inflatable spa, though we generally aren't using it every single night, and don't keep it very hot. I have seen CC start to build up on the occasions we use it every night, and so I can see how with heavy usage (daily long, hot soaks) this could be a factor. Alternatives also include opening an outdoor spa to the sun or adding a UV system.

It wasn't really the mention of MPS that bugged me, it was that it said to add MPS every week, rather than adding if you had high CCs. Adding stuff based on testing, not blindly, is what TFP is all about, right?

Spas/hot tubs get a lot of use for the water volume and this ensures the water stays sanitary.
But if you're regularly testing FC and CC, you shouldn't need to "shock" on a regular basis. Again a generic calendar based series of chemical additions as opposed to testing based additions is what bugs me on that sticky.

Obviously you generally need to add chlorine or another oxidizer (such as MPS) after each use, to oxidize waste created during the soak, which isn't something you do in a pool, but this was mentioned clearly in the sticky and isn't the same as a calender based "shock". Adding after each soak is what will ensure it stays sanitary, not a once a week addition.

Dry acid is not recommended for pools due to the buildup in sulfates. Sulfates can damage SWG's, plaster and concrete. You don't have these issues in a fiberglass standalone spa/hot tub that replaces water every few months. So dry acid can be used in hot tub/spas and some folks find it easier handling and safely storing dry acid.
I see. I was under the impression that sulfates were bad for metals, and so could damage heaters since they have a metal core, such as in this post. In fact, you yourself said they can increase likelihood of corrosion in metals in this post. Would that not include the metals in heaters found in spas? It appears it's more for SWCG plate corrosion, but many people will add a SWCG to their standalone spa (I plan to), and so shouldn't use MPS.

It is mentioned in the wiki -

I always forget about those articles. Seems that that could use some additional information too, especially as it's located in "further reading", which to me means "more advanced", but that might just be me.

Write up your techniques and let's see how it works. There are many ways to keep a spa/hot tub sanitary and safe.
I will certainly do this once I get at least one water cycle (2-3 months) in our first "real" spa at our upcoming new house, which will likely have far heavier usage than our current inflatable spa has ever had.
 

ajw22

Gold Supporter
TFP Guide
Jul 21, 2013
11,633
Northern NJ
I was thinking if you happened to get a positive CSI you'd start scaling, but after playing with poolmath I realized you'd likely need a fill CH of like 500+ for this to really start being a concern, since your TA will almost certainly have to always be right around 50.
Scaling does not happen overnight. If you replace water every few months in a spa then it will not become an issue.

I suppose this depends on the usage. I haven't seen an issue with CC buildup with our inflatable spa, though we generally aren't using it every single night, and don't keep it very hot. I have seen CC start to build up on the occasions we use it every night, and so I can see how with heavy usage (daily long, hot soaks) this could be a factor. Alternatives also include opening an outdoor spa to the sun or adding a UV system.
You are hitting on the problems of creating one size fits all directions for spa care when there is a wide range of spas/hot tubs with greatly different bather loads and uses.

It wasn't really the mention of MPS that bugged me, it was that it said to add MPS every week, rather than adding if you had high CCs. Adding stuff based on testing, not blindly, is what TFP is all about, right?
Many spa users want s simple routine they can follow. TFP is about keeping things as simple as possible.

But if you're regularly testing FC and CC, you shouldn't need to "shock" on a regular basis. Again a generic calendar based series of chemical additions as opposed to testing based additions is what bugs me on that sticky.
It is simple. You are an engineer. What is simple to you is not simple to others. Keeping a small body of heated water that is covered and has high bather loads sanitary is harder then an outdoor pool. People buy standalone spas because they want something simple they can enjoy.

I see. I was under the impression that sulfates were bad for metals, and so could damage heaters since they have a metal core, such as in this post. In fact, you yourself said they can increase likelihood of corrosion in metals in this post. Would that not include the metals in heaters found in spas? It appears it's more for SWCG plate corrosion, but many people will add a SWCG to their standalone spa (I plan to), and so shouldn't use MPS.
First of all you will not have damaging accumulation of sulfates if spa water is replaced every few months. Secondly many modern standalone spas heaters are a different design then the copper coils in pool heaters. Many spas use waste heat from the circulation motors to heat the water.

Be careful about taking what you read about pool care and extrapolating it to standalone spa care. The equipment is different. The uses are different. The water volume and bather load are different. The environment the spa lives in is different. The basic water chemistry is the same.