Nature 2 and OxyShock

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TreeFiter

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Jul 2, 2012
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Saugerties, NY
I work with a lot of hot tubs that use the Nature 2 system. In these tubs we add OxyShock once a week and adjust the chemistry. I'm a bit fuzzy on how it all works. What does the OxyShock do? What does the Nature 2 do?

I have found that I often have to supplement with granular chlorine in some tubs to keep them from getting funky, even with the Nature 2. Is this typical?

I have also noticed that adding OxyShock will lower the pH. Is it reasonable to rely on this to lower pH in a tub?

When testing the chemistry of a Nature 2 tub, what should I expect to see? For example, will I see a change in the results if I add OxyShock? Should I ever see Chlorine readings if I haven't added chlorine or bromine?

I have one tub that is a total mystery to me. It has a Nature 2, and it is serviced weekly. I add OxyShock, adjust pH, and typically that is all it needs. For some reason, I get a reading for Chlorine. Over the past few weeks I have seen the Chlorine levels continue to climb to rather high levels (10ppm). What could be causing this?
 
TreeFiter said:
I work with a lot of hot tubs that use the Nature 2 system. In these tubs we add OxyShock once a week and adjust the chemistry. I'm a bit fuzzy on how it all works. What does the OxyShock do? What does the Nature 2 do?
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OxyShock is non-chlorine shock (potassium monopersulfate aka MPS, probably at 43% concentration). It is an oxidizer, but when used in a hot spa along with silver ions, it is also a disinfectant. Nature2 provides the silver ions. It is an EPA-approved disinfecting system, but not the way you are describing using it. See the Nature2 Spa Manual and note that you are supposed to check the MPS level before your soak and add more if it's too low AND you are to add MPS after your soak. You shouldn't be adding it just once a week unless 1) you are only soaking once a week and 2) the MPS level is lasting through the week (it probably isn't, though it does last longer than chlorine if there is nothing left to oxidize since it does not outgas).

TreeFiter said:
I have found that I often have to supplement with granular chlorine in some tubs to keep them from getting funky, even with the Nature 2. Is this typical?
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That is normal. First, use enough MPS (see my answer above). If you still get some funkiness, then add chlorine. MPS oxidizes some chemicals, but not all the ones that chlorine does (and vice versa). Think of them as complementary. So shocking with chlorine every week or so is typical.

TreeFiter said:
I have also noticed that adding OxyShock will lower the pH. Is it reasonable to rely on this to lower pH in a tub?
Click to expand...
That is normal since MPS is acidic. Yes, you can count on this to keep the pH down and may need to adjust the TA level so that you strike a reasonable balance since higher TA outgasses more carbon dioxide that cause the pH to rise. So if you get your pH to be fairly stable, then the net effect of the MPS would be a slow drop in TA over time, though if you don't compensate for that then you'll find the pH starting to drop as the TA level gets lower.

TreeFiter said:
When testing the chemistry of a Nature 2 tub, what should I expect to see? For example, will I see a change in the results if I add OxyShock? Should I ever see Chlorine readings if I haven't added chlorine or bromine?
Click to expand...
MPS will show up as CC in DPD chlorine test kits and will show up as FC (if there is any chlorine at all; or as CC if there is not) in FAS-DPD chlorine test kits. There is a Taylor K-2042 test kit that removes the interference from MPS letting you measure chlorine and MPS levels separately.

TreeFiter said:
I have one tub that is a total mystery to me. It has a Nature 2, and it is serviced weekly. I add OxyShock, adjust pH, and typically that is all it needs. For some reason, I get a reading for Chlorine. Over the past few weeks I have seen the Chlorine levels continue to climb to rather high levels (10ppm). What could be causing this?
Click to expand...
See above as that is normal. MPS will register as either CC or FC depending on the test kit. If you see this level climb, that's MPS building up, perhaps because the tub isn't getting used so there is nothing to oxidize, though usually MPS won't last much more than a week.
 
Thank you so much for your response chem geek.

We only add MPS once per week because we can only be there once per week. We use test strips to test the chemistry (I know Test Strips suck). I have noticed on some tubs that when I add MPS, I will see a reading of CC. On the mystery tub, I am seeing a reading for FC. It is quite likely that the tub doesn't get used, and it is kept at a low temperature (around 65). So it would make sense that we just keep adding MPS and very little or none of it is being consumed.

If I understand correctly, it seems that if I don't see a CC reading on my test strips, I probably haven't added enough MPS.
 
For the DPD chlorine test (the one that is shades of pink/red), MPS will show up as CC, but it's possible that very high levels might bleed through and show up some as FC. Really high levels might bleach out the DPD just as chlorine does.
 
You can use any reducing agent, such as hydrogen peroxide. Roughly speaking, an equal volume of 3% hydrogen peroxide counteracts the chlorine from an equal volume of 6% bleach so you can use The Pool Calculator to roughly figure out how much you need to add. If your test kit says 10 ppm FC in 350 gallons, then that would be 7.3 fluid ounces of 6% bleach so the same volume of 3% hydrogen peroxide.

Note that if you overdose with the hydrogen peroxide, then when you add an oxidizer back to the spa it won't initially show up as it will get consumed by the remaining hydrogen peroxide until that gets used up.
 
This thread has been idle a while, but I've come up with a question that fits right in here. I recently learned about Bromine and Bromide and how we can use an oxidizer to convert Bromide to Bromine. So it got me thinking about how the Nature 2 system works. I don't really understand the chemistry of how Silver Ions can sanitize water. I would imagine that as they do their thing, they get "used up." I'm drawing some parallels from Bromine-Bromide. So if the Silver gets used up, I'm thinking that the Oxidizer (MPS) is freeing up the Silver Ions so they can once again do their thing. I've noticed that in some of my tubs, I'll see a reading for FC in tubs that use Nature 2 and MPS (much like the mystery tub I described above). I've started to experiment with tubs that didn't show this. If I add MPS and wait several minutes, I will start to see FC readings climb. It is almost identical to what I see when I add MPS to Bromine Tub. So it seems to me that the MPS is driving a change, the result of which manifests itself on a test strip as FC.

Does this make sense, or am I seeing things that aren't really there?
 
The exact mechanism is not know, though loosely speaking silver catalyzes a reaction that damages both cell membranes and DNA. This paper has some discussion of what is known about the details of the mechanism.

Silver alone is not considered sufficiently effective, but in combination with MPS and the higher water temperatures in a spa, acceptable kill times can be achieved.
 

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Hmm...I was really hoping to find out that there is a reaction that is reversed by adding an oxidizer. It just seemed to make sense with what I am seeing.

But I guess this brings up the next question. If the silver ions are not used up, why is it necessary to replace the Nature 2 cartridge roughly every 4 months? Shouldn't the silver ion concentration remain constant as long as there isn't significant water replacement?
 
I am not sure of the exact science behind it but I like using my nature2 in my tub.
I shock after each use and if we do not use for a week I shock once a week at a minimum. There are times where it starts to smell a little "funky" and I will throw a capful of chlorine in there. I balance the ph and TA with my Taylor kit from the pool.

I find that the test strips for nature2 are more useless than the normal 7 way strips for the pool. Just make sure that you add chlorine when you change the nature2 cartridge to activate it.


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bdex, what you just described is almost exactly what I typically do. I didn't realize there was even a test strip specifically for the Nature 2. Is it supposed to measure the concentration of Silver Ions?

You bring up another interesting idea. Why is it necessary to "activate" the Nature 2? This feels like another supporting argument to my hypothesis that there is some reaction that requires reversal through the addition of an oxidizer (either MPS or Chlorine).
 
Silver isn't an oxidizer. You still need to add something to oxidize bather waste. The oxidizer is not reacting with the silver in any way, but it is reacting with the bacterial cells and viruses damaged by the silver (as well as other organic waste that didn't react to the silver).

There is always water replacement in a spa. Someone getting out of the tub takes a noticeable amount of water along with them.
 
Jason, I'm still not quite convinced. It is recommended that the water be changed in a spa, several times each year because of chemical build up. This wouldn't be necessary if there were as much water replacement going on as you suggest above.

Also, what is going on when you "activate" the silver ions? There must be some sort of interaction between the chlorine and the silver compound, otherwise this step wouldn't be necessary.

Silver is vulnerable to oxidation (this is why jewelry needs to be cleaned). Why wouldn't this be the case if silver ions were in solution with oxidizing agents? We see what happens when we have Iron or Copper present and exposed to oxidizers...they oxidize and leave staining behind. So why wouldn't Silver behave in a similar manner.
 
Hum, silver does have three oxidation states. I suppose that this could have something to do with controlling which of those oxidation states it is in. Researching a little, the higher oxidation states of silver are more effective bactericides, and also less stable than the lower oxidation states.
 
The silver ion does attach itself to some organics as was noted in the paper Jason linked to. Thiol groups in enzymes and proteins may be affected by silver ion and there may be other hydrogen bonding going on and silver also affects bacterial membranes. So while some silver is removed from water replacement, some may also get filtered out along with dead skin cells and other organics with which silver may loosely bond. It doesn't get used up very quickly, but the purpose of the Nature2 cartridge is to continuously supply a small amount over time. The fact that the rate of release is not carefully controlled is a reason why it is not recommended for use in pools due to possible staining and the fact that it does not provide disinfection on its own.

This post describes how persulfate reacts with silver ions to produce both sulfate radicals and divalent silver ions. These along with monopersulfate (MPS) at hot spa temperatures provides fast enough disinfection to pass EPA DIS/TSS-12. While there appears to be clear chemical mechanisms for potential disinfection with persulfate, the mechanisms for monopersulfate (MPS) even with silver ion are not well understood, but at hot temperatures might be similar (see this post for more details).

So the bottom line for proper disinfection using Nature2 one must have the following 3 ingredients: 1) silver ions, 2) monopersulfate (MPS), 3) hot temperatures. Note that the silver ions are not oxidizers so for oxidizing bather waste the MPS is needed and because MPS isn't an ideal oxidizer, adding chlorine once a week or so is usually needed to keep the water clear.

By the way, the chlorine "activation" of the Nature2 cartridge is about oxidizing the cartridge to release silver ions faster after a fresh refill since there will be no initial silver ions in the fresh water.
 
I was reminded of this thread today when I checked on a Hot Tub with a Nature 2 in it. I actually just acquired this customer because their daughter was getting a rash after using the tub. So they fired their old Hot Tub guy, and called me. I am reasonably certain that there has been no Chlorine or Bromine used in this tub. It has been strictly Nature2 with OxyShock. So what I saw today that made me think of this thread was a very high FC reading. This was on a test strip, but it raises a question I've asked a few times, but I don't think I ever found an answer to. What does the FC reading really tell us? It can't be a direct reading of Chlorine or Bromine concentrations if it provides readings in water containing neither Chlorine or Bromine.

I've been told that MPS will sometimes cause a false reading as FC, but I've experimented with MPS, and I was unable to produce such a false reading. When MPS is present, I always get a reading for Total Chlorine, but not Free Chlorine.

I keep coming back to the idea that there must be some property being measured by the test strip that is interpreted as FC or Bromine, which is also detected in the presence of Silver Ions.

The FC reading seems to be proportional to the amount of MPS added to the tub. A week ago I added a heavy dose of MPS, and now the FC reading is very high. Much like I might expect to see in a Bromine tub with a big Bromide bank.
 
It's more complicated than that with the FAS-DPD kit because MPS will react with the FAS-DPD reagent and with the R-0003 potassium iodide to produce iodine but not with the DPD dye. So if there is no chlorine or other DPD-reactive oxidizers in the spa at all, then you will get no pink and call that 0 ppm FC. When you then add R-0003 then the MPS reacts with potassium iodide to produce iodine that reacts with DPD to show pink/red during the CC test. The following table shows the possible situations:

. FC .. CC .. MPS measures as
... 0 . >=0 . CC because you don't see pink/red during the FC test but will see pink/red during the CC test from MPS reacting with iodide to produce iodine
. >0 . >=0 . FC because the MPS uses up the FAS-DPD during the FC titration
 

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