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Nature2 & Mps: This Much Divergence In Amounts To Use?


InHotH20

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I recently got my new Hot Spring Grandee delivered and I'm loving it. Since it has a good CD ozone unit, I'd prefer to use the Nature2 low chlorine option. While I know each user will need to test the water daily in the beginning to determine how much sanitizer to use, I'm surprised by the huge variations in the amount of MPS (and dichlor) recommendations from the following three sources:

Hot Springs manual for my 500 gallon Grandee:

Use 2 tablespoons of MPS before each use

(Alternatively, 1 teaspoon of dichlor before each use)

No mention of using anything after using the tub

Nature2:

Use 2 tablespoons of MPS before AND 2 tablespoons MPS after each use

(Alternatively, use 2 tablespoons of MPS before AND 2 teaspoons of dichlor after each use)

Hot Springs dealer, typed instructions:

Use 2 - 4 tablespoons of MPS before each use, AND 1 to 4 tablespoons dichlor (yes, tablespoons) after each use

Which of these options do you think is closest to reality for the "average" user?

Finally, for those using Clorox, the Hot Springs manual states on p. 54 that "use of a liquid or any type of compressed bromine or chlorine... WILL damage your spa and is specifically not covered under the terms of the limited warranty". Strange.

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According to the Nature2 manual, the MPS level is to be tested and if low then add 1 tablespoon of MPS per 250 gallons before each use. After use, 1 tablespoon of MPS per 250 gallons is to be added. These amounts are designed to have a specific sanitation level -- it is not based on what is needed to oxidize bather waste based on the number of person-hours of soaking. The dosage in a typical 350 gallon spa of around 2.8 tablespoons handles around 72 person-minutes of soaking -- so roughly 1 person for an hour or 2 people for 30 minutes. This is without an ozonator.

If you don't have an ozonator, then the rough rule of thumb we've found on this forum to be reasonable accurate in a hot (100-104F) spa is the following dosing per person-hour of soaking: 3-1/2 teaspoons of Dichlor or 5 fluid ounces of 6% bleach or 7 teaspoons of non-chlorine shock (43% MPS). With your ozonator, you would likely use lower amounts assuming you use the tub every day.

As for the spa manufacturer recommendation not to use bleach or solid forms of chlorine or bromine, this is based on the fact that bleach alone without initial Cyanuric Acid (CYA) in the water would be too harsh on spa components, mostly on hot tub covers. We do not recommend using bleach alone, but rather to start out using Dichlor until one has cumulatively added around 33 ppm FC to get 30 ppm CYA, usually around one week of dosing, and then switch to bleach after that (plus one day a month of Dichlor to maintain the CYA level). As for solid forms of chlorine, that would be Trichlor (usually) and that is too acidic and dissolves too quickly to be used in a spa. Not sure about the bromine tab restriction since those are quite common in floating dispensers.

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"Attention: (Nature2 is) Not to be used with product containing bromine, sodium bromide, or biguanides. If these products are being used, be sure to drain and refill the spa with fresh water.."

Nature2 Spa Compatibility

WARNING: Watkins Manufacturing Corporation DOES NOT recommend the use of any floating chemical dispenser. Damage to the spa shell or components caused by a floating chemical dispenser is specifically not covered under the terms of the limited warranty.

The spa shell easily can withstand the effects of a properly administered sanitizer. Floating dispensers can become trapped in one area and cause an over-sanitization (or chemical burn) of that particular area. If the dispenser setting is too high, the high concentration can discolor the spa shell and damage the underside of the cover.

Automatic floating dispensers have a tendency to either over-brominate or under-brominate as the rate of erosion varies greatly.

The floater may allow pieces of the highly concentrated sanitizer to fall out and settle on the floor or seat of the spa shell. These pieces of sanitizer will chemically burn (blister) the spa shell.

Although your spa shell is specifically designed to resist the effects of spa chemicals, no spa surface can withstand this type of highly concentrated chemical. Remember, chemical abuse is specifically not covered under the terms of the warranty.

http://www.hotspring.com/pdfs/2009_manual.pdf

I have found this to be true. Floaters are poorly designed and tablet quality varies greatly. Some tabs dissolve slowly with little or no dust or precipitate.

Some tabs dissolve rapidly and may even break apart and fall onto the bottom of the tub below the floater.

I will usually modify a floater by closing it all of the way and then drilling several small holes about 2 inches above the bottom. This reduces the water transfer, which slows dissolution and it also prevents any precipitate from falling to the floor of the tub.

You have to be careful not to use too many tabs in a modified floater. Usually one or two will be enough. You also have to be careful when opening the floater, as there might be some concentrated bromine or chlorine.

Open over a bucket or other safe area to catch the water that will come out as you open the floater.

I have used a single 1-inch trichlor tab in such a floater, and it worked fairly well. However, I do not recommend trichlor in a floater. Trichlor is too acidic, and most people will not get good results.

Trichlor is usually not a good choice for pools or hot tubs. If it is used, it is important to limit its use based on the cyanuric acid level, which will rise rapidly when using trichlor. In most cases, trichlor should not supply more than 20 % of your total chlorine demand.

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Great response Chemgeek. Thank you. Since I have a CD ozonator, I'd likely use less than those amounts listed then. Is my understanding correct that the amount of sanitizer present in the tub is accurate when using MPS if I have a chlorine strips or test kit? I have the Taylor K2006, but haven't yet purchased the special MPS reagent. Is that really necessary to do if I am not concerned whether the sanitizer is chlorine, MPS, or a combination of both?

My plan at this point is to use MPS on a daily basis, and then shock using chlorine 1x a week. If the tub starts getting cloudy or whatever, then I'd also add chlorine.

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If you are going to use the Nature2 with MPS method, then you can use the MPS strips if you want instead of using the Taylor K-2006 (at least for MPS level; you'd still use the Taylor kit for pH, TA, CH). If you use Dichlor-then-bleach, then you'd use the Taylor K-2006 for the chlorine measurement. If you use a mixture, then to remove the MPS interference, you'd need the Taylor K-2042 to distinguish between chlorine and MPS.

So with your plan, you could use the MPS test strips. Nature2 plus MPS is a very common sanitation method, especially with an ozonator. The only issue I've seen on this forum with that is occasional cloudiness that is taken care of by using chlorine to shock (I think this is more common for those without an ozonator). Apparently, the MPS alone doesn't oxidize all of the bather waste OR perhaps people aren't using enough MPS (I can't tell). Some people are irritated by MPS, but then again some people are sensitive to chlorine or bromine so one has to try out a system to see if it works for them.

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Thanks. I'll get the MPS test strips.

Another question: how much do we know about the safety of MPS? I'm not talking about its use as a spa oxidizer, but rather in general? That is, I'm trying to limit chlorine primarily due to the smell, but some others (like my sister who has a chlorine remover on both her drinking and bathing water sources) make claims that chlorine can be carcinogenic. In googling MPS I see that there are some with skin sensitivity. Any other information on MPS safety?

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Chlorine itself isn't the issue by itself, but when chlorine combines with certain organic compounds (and ammonia) it can form certain Combined Chlorine (CC) compounds and some of these are volatile and some are carcinogenic or irritating or hurtful in various ways, though like anything else quantity is a factor since you are exposed to all kinds of oxidizers in the environment (just eating food results in oxidation and creation of free radicals, but you don't hear people saying to stop eating -- the body is constantly in a fight against getting its cells damaged in various ways). MPS won't form chlorinated compounds, but it will oxidize some organics in specific ways so whether those products are harmful or not is hard to say -- in general, they won't be, but with complex organic chemistry a lot can happen. Personally, I think that either the Dichlor-then-bleach or the N2 plus MPS approaches are reasonably safe because with the former one is careful in maintaining low active chlorine levels and to have most of the oxidation occur after the soak while with the latter one is avoiding halogens completely.

The PAN Pesticides info for MPS is here and isn't much help. You can see that hypochlorous acid is similar here though sodium hypochlorite is more serious in concentrated form as shown here. As I said, concentration is everything.

So it's really a personal choice that you'll have to make for yourself. By the way, if you use the Dichlor-then-bleach method where you start your soak with around 1 ppm FC or so chlorine, then you probably won't smell it during your soak. You would add sufficient chlorine after your soak to oxidize the bather waste and that would normally smell except that you won't be in the tub while this occurs. If you open the tub briefly before getting in the next time, then any products that have outgassed can be removed. If you are smelling something strong, then something is wrong.

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So with your plan, you could use the MPS test strips.

Richard, I know that MPS will interfere with combined chlorine tests, but will combined chlorine interfere with an MPS test strip?

If someone had zero free chlorine, 3 ppm of combined chlorine and zero MPS, would an MPS strip read "Low", "OK" or "High"?

I was thinking that if combined chlorine interfered with the MPS test strips, then it would be best to always use the K-2042 when using chlorine with MPS instead of strips.

General note: The Taylor K-2042 measures MPS as ppm chlorine.

MPS Ideal Range: 2 to 4 ppm when measured as chlorine and 10 to 20 ppm when measured as MPS.

MPS reading as MPS = 5 X MPS reading as chlorine. 1

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That's a good question and I don't know the answer. Normally though, the Combined Chlorine (CC) level is low except in the hour or so right after a soak and even then only if there is chlorine in the water. So testing before the soak is probably mostly measuring MPS on the test strip. Yes, the Taylor K-2042 can be used to distinguish between CC and MPS, but that's probably overkill with the N2/MPS system. It's one thing to have an accurate chlorine test to discover accurate chlorine demand until one learns about their spa, but with N2/MPS it's unlikely for much CC to form anyway since there usually isn't chlorine used every day.

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