Mps Shocking Issues

[hrustar]

When I use MPS to "shock" my hot tub, the water ends up looking horrible. Am I doing something wrong? I add about 1.5 oz. to a 425 gallon tub. For example, this weekend, a friend watched my house and used the tub. When I came home, the water wasn't bad, but not really spot on. I added 1.5 oz. of MPS and went to bed. This morning, the water looks very cloudy. This has happened before.

Any ideas? Am I doing something wrong?

FYI my water numbers are typically around or at:

FC 3

PH 7.2/7.4

TA 100

CH 225

CYA 130

Borates: 50 ppm

CSI at or just bellow 0

[Mikey_in_NY]

When I use MPS to "shock" my hot tub, the water ends up looking horrible. Am I doing something wrong? I add about 1.5 oz. to a 425 gallon tub. For example, this weekend, a friend watched my house and used the tub. When I came home, the water wasn't bad, but not really spot on. I added 1.5 oz. of MPS and went to bed. This morning, the water looks very cloudy. This has happened before.

Any ideas? Am I doing something wrong?

FYI my water numbers are typically around or at:

FC 3

PH 7.2/7.4

TA 100

CH 225

CYA 130

Borates: 50 ppm

CSI at or just bellow 0

As far as I'm aware MPS works best when used in conjunction with a Nature2 cartridge. Is this something you're doing, or are you just using MPS on it's own?

[quantumchromodynamics]

With your cyanuric acid level being so high, at 130, you are not keeping enough chlorine in the tub to keep it sanitary.

You should be maintaining at least 7 ppm of chlorine at all times. Are you getting any combined chlorine? The MPS could be reacting to unoxidized contaminants.

Is it possible that your friend had multiple people over to use the hot tub?

You should be using about 1.17 fluid ounces volume of MPS per person-hour of tub use.

The rule-of-thumb that is independent of tub size is 3-1/2 teaspoons of Dichlor or 5 fluid ounces of 6% bleach or 7 teaspoons of non-chlorine shock (43% MPS) for every person-hour of soaking. - chem geek

You should drain and refill and then carefully follow Nitro's Approach to Water Maintenance

[hrustar]

I am using Nature 2. I also plan to drain in about one month.

As for the 7 ppm of chlorine, that seems awfully high. I think the Taylor book suggest 5 ppm but I have to check. I try to keep the FC low, around 1.5 or 2 before soaking, then punch it up with bleach right as I get out.

Last time I tested for combined chlorine (about a week ago) I had zero.

[BigDfromTN]

I am using Nature 2. I also plan to drain in about one month.

As for the 7 ppm of chlorine, that seems awfully high. I think the Taylor book suggest 5 ppm but I have to check. I try to keep the FC low, around 1.5 or 2 before soaking, then punch it up with bleach right as I get out.

Last time I tested for combined chlorine (about a week ago) I had zero.

The reason he suggests a higher chlorine level is due to the high CYA level. CYA will buffer the Chlorine and it takes much more to do the same sanitizing. Thus the Di-chlor then bleach method.

[hrustar]

I am using Nature 2. I also plan to drain in about one month.

As for the 7 ppm of chlorine, that seems awfully high. I think the Taylor book suggest 5 ppm but I have to check. I try to keep the FC low, around 1.5 or 2 before soaking, then punch it up with bleach right as I get out.

Last time I tested for combined chlorine (about a week ago) I had zero.

The reason he suggests a higher chlorine level is due to the high CYA level. CYA will buffer the Chlorine and it takes much more to do the same sanitizing. Thus the Di-chlor then bleach method.

A-ha. that makes excellent sense.

[Dietitian]

Your CYA level is too high, and most of your 3 ppm FC is bound to the CYA. You should have about 30ppm CYA in the tub. At current levels your effective "active" chlorine is about 0.12 ppm

[hrustar]

Your CYA level is too high, and most of your 3 ppm FC is bound to the CYA. You should have about 30ppm CYA in the tub. At current levels your effective "active" chlorine is about 0.12 ppm

If this is true (which I'm not doubting) how come my water has remained crystal clear (with heavy tub use) for the better part of a couple months, despite having the rocket high CYA? What's more, no itching, rashes or biofilm? In otherwords, what signs wold there have been if my FC was indeed that much less than what you propose?

I've only had the clouding issue when adding non chlorinated shock.

THANKS!

[chem geek]

Using Dichlor-only is usually OK for most people for at least 2 months and sometimes 3 or 4 depending on bather load. The higher the bather load, the shorter time the water stays in good shape. With Dichlor-then-bleach, most people are able to go around twice as long between water changes and when they do change the water, they don't notice it being much different meaning that it really didn't get that bad.

It's not the FC that gets lower at higher CYA, but rather the active chlorine (hypochlorous acid) level that does most of the oxidation, disinfection, etc.

[EDIT] P.S. It also depends somewhat on how clean you are in terms of what you introduce into the tub. Every situation is a little different. You can always get lucky. I'm just noting above what is typically reported on this forum. Also note that there seemed to be a somewhat higher incidence of hot tub rash/itch/lung incidents reported on this forum after 1-2 months of Dichlor-only use, but the sample size was too small to be definitive. The most common cause of problems, however, was having very low or no chlorine at all, usually from "alternative" systems. See this post for more info. [END-EDIT]

[Dietitian]

Your CYA level is too high, and most of your 3 ppm FC is bound to the CYA. You should have about 30ppm CYA in the tub. At current levels your effective "active" chlorine is about 0.12 ppm

If this is true (which I'm not doubting) how come my water has remained crystal clear (with heavy tub use) for the better part of a couple months, despite having the rocket high CYA? What's more, no itching, rashes or biofilm? In otherwords, what signs wold there have been if my FC was indeed that much less than what you propose?

I've only had the clouding issue when adding non chlorinated shock.

THANKS!

The water would have likely turned cloudy even if you had not used MPS. The cloudiness is probably a result of the chlorine concentration dropping low enough to allow something to grow in the tub and cloud the water. The MPS you add when you get home may not be enough to combat whatever your friend left in the tub, and the CYA is keeping the chlorine's power so low that the FC is having trouble oxidizing bather waste.

I would drain the tub and begin using Nitro's method, making sure to keep CYA lower, around 30 ppm.

[simonc]

You should be using about 1.17 fluid ounces volume of MPS per person-hour of tub use.

QCD -

How much DRY GRANULAR MPS should one use per person-hour? When I add MPS, I have no idea how much to add.

Also, how much MPS does one need to add to get rid of CCs? To get rid of 1ppm CC per 100 gallons, how much MPS do I need to add?

Is there some type of online calculator to figure this stuff out? Something like the poolcalculator? Or ... does one need to be a chemist? I'm not.

Thanks for the great help you've given me and others on this forum.

- Simon

[chem geek]

It's 7 teaspoons of MPS (43% purity; note that some are less pure; look for potassium monopersulfate content). That's the same as the 1.17 fluid ounce -- QCD meant ounces volume, not literally a fluid. You can measure dry substances in ounces volume as well and unfortunately this is called a fluid ounce since it is normally used for measuring fluid volumes.

For CC, you technically don't need more than 1 ppm FC to get rid of it, but it may take a higher FC to make the CC go away faster. Note that you will normally measure some CC if you add chlorine after a soak so you shouldn't test for CC after a soak. Instead, test for it before the next soak (i.e. the same time you normally test for FC). You can shock to 10 ppm FC to see if that helps to get rid of the CC faster, but normally you won't have much CC by your next soak if you've been using enough chlorine after each soak and have a reasonably hot spa and not too high a bather load.

Note that you can oxidize the CC with bleach if you want to; you don't have to use MPS unless you want to. You can use the Pool Calculator to figure out the amount of Dichlor to get to a certain amount of FC and then just double that quantity to figure the equivalent amount of MPS (assuming 43% purity).

[quantumchromodynamics]

Note: Just go to the answer in blue near the bottom if you don't want to read the technical stuff.

Fluid ounces just means volume. It does not necessarily pertain exclusively to liquids. The general guideline is 7 teaspoons of non-chlorine shock (43% MPS) for every person-hour of soaking. 7 teaspoons equals 1.17 ounces (volume). Whenever I use the term "ounces", I try to identify if the ounces are volume or weight.

3(2KHSO₅•KHSO₄•K₂SO₄) + 4NH₃ --> 15K⁺ + 2N₂ + 9H⁺ + 12SO₄^2- + 6H₂O

3 moles of MPS will oxidize 4 moles of ammonia. Molecular Weight (Triple Salt) 614.7 grams per mole.

3 moles of MPS = 1,844.1 grams. 4 moles of ammonia = 14.0067 x 4 = 56.0268 grams

1,844.1/56.0268 = 32.9146

You would need to add 32.9146 grams per 1,000 liters of water per 1 ppm of ammonia (Measured as Nitrogen).

If you are measuring CCs as ppm chlorine, you have to divide the CC number by 5.06 to get the ammonia amount.

Example: If you had 2.2 ppm of CC, you would have 2.2/5.06 = 0.4348 ppm of ammonia. 0.4348 x 32.9146 = 14.31 grams of MPS to oxidize 2.2 ppm Combined chlorine in 1,000 liters of water.

That's 6.5 grams per 1 ppm Combined Chlorine per 1,000 liters. Or, 2.46 grams per 1 ppm Combined Chlorine per 100 gallons of water.

Bulk density of MPS = 35.44 grams per ounce volume.

2.46/35.44 = 0.0694 ounces volume MPS per 1 ppm CC per 100 gallons.

Example: 2.2 ppm of CC in 264.2 gallons = 0.0694 x 2.2 x 2.642 = 0.4033 ounces volume or 14.3 grams of (100 %) MPS or 0.4635 ounce volume (87 %) MPS (43 % Active ingredient).

2.2 ppm of Combined Chlorine will take a total of 1.5 x 2.2 = 3.3 ppm of chlorine to oxidize.

1.8081 ounces volume of 6 % bleach will provide 3.3 ppm in 264.2 gallons of water.

0.3111 ounces of 6 % bleach will oxidize 1 ppm CC in 100 gallons of water.

0.4635 ounces volume of (43 %) MPS = 1.8081 ounces volume 6 % bleach.

1 ounce volume (43 %) MPS = 3.9 ounces 6 % bleach.

1.5 moles of total chlorine will oxidize 1.0 mole of combined chlorine (measured as ammonia (measured as nitrogen))

106.359 grams of total chlorine will oxidize 14.0067 ppm of ammonia in 1,000 liters of water.

7.59 grams of total chlorine will oxidize 1 ppm of ammonia in 1,000 liters of water.

1.545 ounces of 6 % bleach will oxidize 1 ppm ammonia in 100 gallons of water.

1.545 ounces of 6 % bleach will oxidize 5.06 ppm CC in 100 gallons of water.

0.305 ounces of 6 % bleach will oxidize 1 ppm CC in 100 gallons of water.

1 mole of MPS = 2 moles of chlorine

614.7 grams of MPS = 141.812 grams of chlorine (Cl2)

Bleach = 1.8594 grams of chlorine per ounce volume.

17.34 ounces volume of MPS = 76.2676 ounces volume of 6 % NaOCl bleach (5.715 % chlorine by weight).

1 ounce volume (100 %) MPS = 4.398 ounce volume 6 % bleach.

1 ounce volume of (100 %) MPS (49.5 % Active ingredient) = 4.398 ounces volume of 6 % bleach.

1 ounce volume of (87 %) MPS (43 % Active ingredient) = 3.826 ounce volume 6 % NaOCl bleach (5.715 % Cl2 by weight).

_____________________________________________

Answer:

2.8275 grams of (43 %0 MPS) per 1 ppm Combined Chlorine per 100 gallons of water.

0.07978 ounces volume (43 %) MPS per 1 ppm CC per 100 gallons of water.

0.305 ounces of 6 % bleach will oxidize 1 ppm CC in 100 gallons of water.

_____________________________________________

Note: This assumes that the chlorine in the combined chlorine does not participate in the process and is just released as free chlorine. This will provide a free chlorine equal to the combined chlorine after the process is completed.

This also assumes that all of the ammonia is currently combined. An ammonia test kit can be used to get the actual ammonia nitrogen amount.

You can count the chlorine in the combined chlorine as part of the necessary oxidizer demand if you want to.

Assuming that the combined chlorine is NH2CL, you would divide the amount of MPS or chlorine by 3 because the chlorine in the combined chlorine is taking 2/3 of the oxidizer demand.

Here is an interesting reference:

John A. Wojtowicz

Chemcon

Chemistry of Nitrogen Compounds in Swimming Pool Water

Nitrogen–containing impurities (e.g., ammonia, amino acids, creatinine, uric acid, etc.) introduced into swimming pools by bathers react with free available chlorine to form combined chlorine compounds.

Because these compounds do not readily hydrolyze to hypochlorous acid, they are poor disinfectants. In effect, these combined chlorine compounds adversely affect disinfection by consuming free available chlorine.

Ammonia is readily oxidized by free chlorine by the process of breakpoint chlorination. Amino acids are also decomposed by excess free chlorine although at a slower rate.

Creatinine is similarly decomposed but the process is very slow.

Ammonia derived chloramines are inherently unstable in the presence of sunlight because they absorb ultraviolet light. Indeed, monochloramine although stable in the absence of sunlight and free chlorine, is largely oxidized (~67%) to elemental nitrogen in the absence of free chlorine and the presence of sunlight.

It is worth noting that it is urea and not ammonia that is the major nitrogen–containing bather contaminant in swimming pools and spas. Surprisingly, urea does not itself form combined chlorine and also does not appear to affect disinfection.

However, urea has to be destroyed by oxidation because it is a nutrient for bacteria and algae and a source of ammonia chloramines. Oxidation of urea by free chlorine is a slow process that gives rise to transient ammonia chloramines (e.g., di– and trichloramine).

Oxidation of other organic nitrogen compounds by chlorine also forms transient ammonia chloramines.

http://jspsi.poolhelp.com/j_v4n1.aspx

[simonc]

John A. Wojtowicz

Chemcon

Chemistry of Nitrogen Compounds in Swimming Pool Water

It is worth noting that it is urea and not ammonia that is the major nitrogen–containing bather contaminant in swimming pools and spas. Surprisingly, urea does not itself form combined chlorine and also does not appear to affect disinfection.

However, urea has to be destroyed by oxidation because it is a nutrient for bacteria and algae and a source of ammonia chloramines. Oxidation of urea by free chlorine is a slow process that gives rise to transient ammonia chloramines (e.g., di– and trichloramine).

Oxidation of other organic nitrogen compounds by chlorine also forms transient ammonia chloramines.

QCD -

Thanks for the bottom line answer and your detailed explanation. Although I don't have a background in chemistry, you explained it very well and I appreciate you taking the time to show how you got to the bottom line.

I was especially interested in the information you gave us provided by Mr. Wojtowicz (see quote above).

Again, I don't really understand chemistry (and the various names of the chemical compounds produced) but it seems to imply that Chlorine is NOT the BEST oxidizer for urea. Am I correct in my reading of the statement?

If so, what is the best oxidizer of urea? Is it MPS? The MPS oxidation process doesn't produce CCs. It seems that using chlorine to get rid of urea does produce CCs? (I'm assuming that "ammonia chloramines" is a CC???) Please pardon my ignorance. (When I bought my tub I didn't know that I need to know anything except how to sign my name on the check I wrote the dealer.)

Is an ozonator the BEST oxidizer of urea? My ozonator is probably not working (4+ years old). Maybe I should get it replaced?

I've been using the diclor-then-bleach method in my tub. It seems to be working very well for me.

- Simon

[chem geek]

Surprisingly, there has been very little research on the chlorine oxidation of urea. However, based on the latest research by Dr. Ernest "Chip" Blatchley of Purdue, chlorine oxidation of urea is very likely to form combined chlorine, specifically chlorourea (not sure if it's mono, di, etc.) and that this gets measured in the DPD test (and FAS-DPD) as CC. It takes some time, up to an hour or so at cooler temps (near 77F) for the chlorourea to form and it takes days at that cooler temp for chlorine to oxidize this chlorourea. See this link and this link.

In practice, one doesn't see the kind of CC implied by the above in either residential pools or in residential spas. I'm going to speculate here, but there are two reasons for this. First, is that the UV in sunlight for outdoor pools may accelerate the oxidation either by direct interference with urea or more likely by production of free radicals (including hydroxyl radicals) from the breakdown of chlorine that produce chain reactions that help to oxidize the urea. Also, residential pools have fairly low bather loads. Second, is that the chlorine oxidation rate of urea is VERY temperature dependent. This link to an old 1908 paper implies this latter temperature dependence. So in spas, the chlorine oxidation of urea is probably very fast, in a matter of hours, which would explain what we see in actual residential hot tubs.

The actual mechanism for the chlorine oxidation of urea is unknown though Wojtowicz has speculated on this. However, even producing dichloramine and nitrogen trichloride, these will combine and get further oxidized just as is done with normal chlorine oxidation of ammonia. I describe some of this in this post.

An ozonator should in theory oxidize better than chlorine. As to whether it actually oxidizes urea quickly enough, I don't know, but it is probably going to do so faster than chlorine. I don't know how well or quickly MPS oxidizes urea. It generally oxidizes nitrogeous organics of that type, just as it does with ammonia, but I don't know how quickly.

If you aren't having any problems with your current situation using Dichlor-then-bleach and you normally add chlorine after your soak so most oxidation and intermediate by-products are produced when you are not in the tub and you vent the tub before you go in the next time, then I'm not sure why you are concerned. If you wanted to reduce disinfection by-products, then using an ozonator will help as it will oxidize some of the bather waste before chlorine gets a chance to. This is also true with MPS to some extent (at least for ammonia; possibly for urea).

By the way, if you actually had any significant amount of nitrogen trichloride being produced, you would most definitely smell it. It is detectable as low as 20 ppb and it is very smelly and irritating and is the chloramine of most concern. The dichloramine threshold is around 100-500 ppb (0.1-0.5 ppm) and also smells bad. So if you aren't smelling much, you probably have fairly low disinfection by-product formation (assuming you check to smell your tub after you add chlorine to the tub when you get out and then monitor it). With the CYA moderating chlorine's strength, the monochloramine formed will last longer, there will be more dichloramine, and less nitrogen trichloride, but the monochloramine and dichloramine get fully oxidized so really it is the nitrogen trichloride that is of the most concern and fortunately that is minimized due to the low active chlorine level.

[quantumchromodynamics]

Again, I don't really understand chemistry (and the various names of the chemical compounds produced) but it seems to imply that Chlorine is NOT the BEST oxidizer for urea. Am I correct in my reading of the statement?

If so, what is the best oxidizer of urea? Is it MPS? The MPS oxidation process doesn't produce CCs. It seems that using chlorine to get rid of urea does produce CCs? Is an ozonator the BEST oxidizer of urea? My ozonator is probably not working (4+ years old). Maybe I should get it replaced?

I've been using the diclor-then-bleach method in my tub. It seems to be working very well for me.

- Simon

Outdoor pools exposed to sunlight and low to moderate bather loads do not have too much problem with chloramines due to the Ultraviolet light, which helps oxidize the chloramines.

Most private pools and spas that are properly maintained and have low to moderate bather loads will do well with only chlorine. The dichlor then bleach method is a good choice for many people.

Some people feel that they get worthwhile benefits from supplemental oxidation from Ozone, MPS or UV.

Indoor pools and spas that get heavy use can usually benefit from alternative oxidation methods, such as Ozone, Ultraviolet or MPS.

Heavy bather loads in an indoor pool are very difficult to manage with just chlorine due to the chlorinated byproducts that are formed, such as chloramines and Trihalomethanes (Such as CHCl₃ (chloroform))

[simonc]

Some people feel that they get worthwhile benefits from supplemental oxidation from Ozone, MPS or UV.

Indoor pools and spas that get heavy use can usually benefit from alternative oxidation methods, such as Ozone, Ultraviolet or MPS.

QCD -

Thanks for helping me with this issue.

I would say my tub is not "heavy use". 275 gallons - my wife and I use it in the evenings (15-20 minutes) about 3 or 4 times a week.

I have a small container of MPS. I guess I'll continue using it. When it runs out, I probably won't rebuy it.

My water smells/feels fine. My CC level is usually around 1ppm. After shocking with chlorine, I get it down to about 0.5ppm. It doesn't seem to go below that. I'm fine with less than perfection.

- Simon

[simonc]

If you aren't having any problems with your current situation using Dichlor-then-bleach and you normally add chlorine after your soak so most oxidation and intermediate by-products are produced when you are not in the tub and you vent the tub before you go in the next time, then I'm not sure why you are concerned.

By the way, if you actually had any significant amount of nitrogen trichloride being produced, you would most definitely smell it.

Chem Geek -

Thank you for your helpful response.

I guess I don't really have a "concern" ... my water smells/feels fine. I was more interested in finding out if one method of "shocking" to get rid of CCs was more effective than another.

I appreciate you pointing out that reactions with chlorine happen much faster in a hot tub than they do in a swimming pool, making chlorine a faster oxidizer in tubs.

For now, I'll probably rely on a combination of chlorine shock and MPS shock to handle CCs. When my supply of MPS runs out, I probably won't rebuy it and just stick with chlorine.

- Simon