How does MPS work as a shock

[BC]

As I understand it from this forum, MPS is not really effective in lowering cc once it's there as using Chlorine to reach a break point to effectively reduce the chloramine.
recommended usages then:
Use on a regular basis as a preventor.
Use with indoor spas to reduce chlorine smell.
But how does it work in helping preventing high levels of CC counts...or how does sulfate interact with all the waste that contributes to CC?
Thanks

 

[chem geek]

It's not the sulfate, but the persulfate, HSO₅^-, that is the primary oxidizer due to its extra oxygen that gives it a fairly high oxidation potential. It can actually oxidize monochloramine somewhat, but it works faster to oxidize ammonia before it becomes monochloramine. Of course, chlorine reacts with ammonia pretty darn fast as well. Both chlorine and MPS are selective oxidizers so though they somewhat overlap in what they oxidize, they also oxidize different chemicals and at different rates. Generally, we don't recommend using MPS since it is not normally needed since you need chlorine for sanitation anyway and it is a fine oxidizer by itself. However, in a residential spa the bather load is high due to the low water volume so having an additional shock with MPS can be helpful at times though is not always necessary.

MPS with Nature2 and specifically the silver ions from Nature2 and also only at hot spa temperatures can also be used as a sanitizer. It's more expensive then the Dichlor-then-bleach method, but for those who want to avoid chlorine for whatever reason, it's an option. Nevertheless, one usually needs to shock with chlorine weekly with this system since MPS alone doesn't seem to do as good a job at keeping spa water clear as chlorine.

You can read more about potassium monopersulfate in this document from Dupont.

Richard

 

[MikeM1]

Hey Richard.... Would excessive MPS cause Oxygen Bubbles/Foam to form when you turn the jets on? In my Tub I use the Nexa SWC and it works great! If I use to much MPS it looks to cause a lot of Oxygen bubbles when the jets turn on and they disappear and go away when the jets are off. Just wondering. I drain and refill every 3 months and at the half way point the bubbles start to get more frequent.

 

[chem geek]

Welcome to TFP!

Too much MPS causing bubbles doesn't sound right to me. Usually, bubbles (foaming) are from soap-like substances and they are reduced if you keep the Calcium Hardness (CH) at around 120 ppm or so (softer water creates more bubbles from soap; harder water inhibits formation of such bubbles). I suppose there might be something about MPS that enhances bubble formation, but it's not obvious to me what that is. The MPS doesn't just spontaneously form oxygen -- it mostly oxidizes other substances and if there isn't anything to oxidize it mostly hangs around, very similar to chlorine. Having more bubbles halfway through changing your water does indicate that you are adding soap-like materials to your spa. You might not be using enough oxidizer in general, though with the Nexa spa chlorine generator I would think it is producing enough chlorine to keep up with your bather load, especially if you are adding MPS in addition.

Is there any particular reason you are adding MPS instead of just adding bleach when you need more oxidation after a heavier bather load than the Nexa can handle (or you can run the Nexa longer). I can't find any "grams chlorine per hour" rating on the Nexa so can't tell how much chlorine it adds how quickly. Every person-hour of bather load requires roughly 3-1/2 teaspoons of Dichlor or 5 fluid ounces of bleach or 7 teaspoons of non-chlorine shock (43% MPS) or 9 grams chlorine (Cl₂ equivalent) to oxidize the bather waste (if you didn't have any other form of oxidation such as your Nexa system or an ozonator). Also, with the Nexa system, I don't see where they start off with any Cyanuric Acid (CYA) in the water and that can make the chlorine too strong and wear on equipment and hot tub covers and be harsher on skin and product more nitrogen trichloride. Did you start off using any Dichlor initially after a fresh refill or do you just start with added salt and the Nexa system?

 

[MikeM1]

I start out with 400 Gallons of water from the softener and then run it through a water filter to be extra sure it is good clean and clear water. My well has a very high level of hardness. Then I add the dead sea salt to get my salt up to 1500 or a little higher. I work then on getting the calcium hardness around the 150 range. Next is to get the TA up to around the 50 range and check on the PH and try get that around the 7.8 range. From reading on the boards here and elsewhere I have started to add some Gentle Spa to get some borates in the water as well. The tub temp is around the 102 to 103 range. CYA is zero. I do have some dichlor around from before i started to use the nexa system.

My daily routine is to check with dunk sticks to get a general idea and once a week I use the Taylor drop test to get a better idea of whats going on. I put in 1 tablespoon of MPS after each session in the tub. Sessions are only at night time for one cycle of the jets. 2 person bathing load very rarely do we stay in longer then that. Time is about 10 Minutes. From reading on some other forums the bubbles I get are Oxygen bubbles from agitation of the water and a chemical reaction is happening from the jets agitating the water. Stop the jets and no more bubbles.

Is there any particular reason you are adding MPS instead of just adding bleach?

I have been following the instructions that came in the box. They just say to add some MPS before and after to help with the sanitation. From my observations I didn't need it before or after since the Chlorine doesn't drop that much. I started to see that with a few longer times we did spend in the tub ended up dropping the Chlorine down to zero. So... I set the timer to just bump up the creation of chlorine just as a precaution and from the reading I did on here and elsewhere the MPS was an ok sanitizer. So... I just started to add a little and all seemed well till i started to get excessive bubbling and foaming.

 

[MikeM1]

Richard... You still out there?

 

[chem geek]

Yup, still here. So what you are doing sounds reasonable and yes, the bubbles/foaming come from agitating the water as with aerated spa jets. However, the persistence of bubbles/foam is going to be related to the amount of soap-like substances in the water. It won't persist in pure water. It's certainly possible that there is something in the non-chlorine shock causing the problem, but I can't figure out what that would be so I'm going with the simpler explanation (Occam's Razor) that the cause is from excess soap in your swimsuit or on your skin that builds up over the months of using the spa.

Since your system seems to work reasonably well without having to add extra oxidizer, you could certainly try cutting back on the MPS and instead adjust the Nexa to handle your bather load. If you need extra oxidizer, you can use 6% Clorox Regular bleach instead. Just note that you need to be careful about the pH rising too much and may need to lower your Total Alkalinity (TA) level to help with that, and also the 50 ppm Borates from the Gentle Spa -- both things you say you will be doing. I suspect that the 50 ppm Borates might also help reduce the amount of foaming, similar to the higher CH as it reduces the surface tension of the water that is needed for soap bubbles to stay formed.

 

[MikeM1]

I'll be refilling the Tub when I get home from the holiday vacation. Tomorrow or the next day and I'll post some updates after that.

 

[BC]

Yup, still here. So what you are doing sounds reasonable and yes, the bubbles/foaming come from agitating the water as with aerated spa jets. However, the persistence of bubbles/foam is going to be related to the amount of soap-like substances in the water. It won't persist in pure water. It's certainly possible that there is something in the non-chlorine shock causing the problem, but I can't figure out what that would be so I'm going with the simpler explanation (Occam's Razor) that the cause is from excess soap in your swimsuit or on your skin that builds up over the months of using the spa.

Hi Richard - Where do you come up with these things? Is this somehow related to the approach as the K.I.S.S. method used in other disciplines? I have to remember this for my work.

 

[MikeM1]

Richard. I just found out I have an Ozone Generator. It's a Del CDS-16 OEM it came with my spa. No Literature in the care package about it. I pulled off the cover when I started to hear some growling noises. Could not find the source as it went away. I noticed it on the right side as I was putting screws back into the cover.

Now with an Ozone Generator as a Sanitizer there is no need for MPS then? Since the Chlorine will be good in conjunction with the Ozonator? Looking for a Manual right now for it. Looks like there are no settings just turn it on and go.

 

[chem geek]

If the ozonator were working properly, then you wouldn't need to use as much supplemental oxidizer (either MPS or bleach). You might still need to add some, depending on bather load and strength of the ozonator. It's hard to measure when using MPS since it can falsely read as Combined Chlorine (CC).

If you just use your SWC and use added bleach after a soak, then you can measure the Free Chlorine (FC) at the start of the next soak and see that it is a reasonable residual. If it's too high, use less bleach; if it's too low, use more bleach. Then, once knowing that needed extra oxidizer level, you can use MPS instead if you want to, though it is more expensive and bleach would work just as well.