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How do I use MPS?


Susanj

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I've posted here before about our hot tub at our vacation rental which gets used heavily in summer (in the mtns).  Guests stay anywhere from 4 to 7 nights.  Capacity is 6-8.

Rather than have our service person come out during a stay, I was planning to leave 2 tbsp of MPS (we have a bromine system) in portion control cups and ask them to add one a day after each use. I am worried about the water getting cloudy and gross during their stay.

I just spoke with someone at the company where we purchased our tub about this and am wondering if you agree with what she had to say.

 She explained that sanitizer kills bacteria but the dead bacteria stays in the water and that can cause cloudiness (it's not the only thing that can cause it though). And in this case, cloudy doesn't mean dirty. Though guests might think so. Shock doesn't kill bacteria. It's not a sanitizer. It's an oxidizer. What it does is it takes the dead bacteria (and skeletons!) and converts it to a gas. That's why you leave the hot tub cover open for 15 minutes after adding it.
 
She said with a floater, there will always be sanitizer in the water, but I've seen the test show none after a bather load. Don't you need MPS to reactivate the bromine then?  She said no, that you only need MPS once a week. That the bromine will regenerate from the floater -it'll just take a little time, but should be good if they use the hot tub daily. 
 
What they could do is add a clarifier to make the water clearer, maybe 2 oz every 3 days , which coagulates the small particles and then the resulting bigger particles can get trapped by the filter.
 
Or I'm thinking if that doesn't work, we could have the guest put in 1 or 2 Tbsp of the granular chlorine?

 

 

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The person you spoke with is missing some points in her understanding of hot tub chemistry. First of all, bacteria is neither the only bather waste you are dealing with, nor even the major portion of it. It is, of course, very important to kill the bacteria, but there is much more that happens. Bathers perspire (the numbers usually cited are 3 pints per person per hour), sometimes leak urine, and also add cosmetics, sun tan lotions, deodorants, etc, all lumped under the heading of bather waste. All of these things need to be neutralized. Some, such as dead bacteria, are particulate solids, and should be filtered out by filters. Filters need to be cleaned regularly to remove this material and to function efficiently. Soluble solids remain in the water, and add to the total dissolved solids, which is one reason the water should be changed regularly.

I think your person is wrong about the dead bacteria staying in the water. I believe that the majority, if not all of the dead bacteria is filtered out if you have good filters and keep them clean. In order for the water to stay clear, all bather waste needs to be neutralized by the active sanitizer or by the oxidizer, or both. With MPS oxidizer, which can neutralize bather waste directly, you probably get a dual effect. However, MPS tends to convert sodium bromide into active bromine (hydrobromous acid) at a much faster rate than it neutralizes bather waste directly, so the probability is that even if bather waste is fairly high, the majority of the MPS will result in active bromine, which will then neutralize the bather waste.

In the bromine three step method, which you are using, the correct procedure is to have the floater set so that the bromine ppm will remain steady during the periods when there is no bather use of the tub. So for instance if you go a few days or a week without anyone renting the bromine will remain level. Then, after each time the tub is used, an amount of oxidizer should be added to exactly neutralize the bather waste, and this will depend on how many users, for how long, at what temperature, and a few other factors.

In your situation, this amount is practically impossible to determine, is probably not the same every day, and you certainly can't expect your guests to figure it out. I think your idea is sound, though. The only question I have is how much to put in the containers for them to add every day. That should be determined on average usage, perhaps. I think it can best be determined by trial and error. To find out would require frequent testing which may not be practical in your situation. So, for example, if the starting bromine ppm is 6, and you have them put 2 tablespoons of MPS in after soaking, and then an hour or two later, or the next day, the bromine ppm is still 6, then you know the MPS effectively and exactly reduced the bather waste. If the ppm goes up then there was too much MPS and if the ppm goes down, then too little MPS.

Hope this is a little helpful.

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Thank you!  

We did determine over the winter by trial and error that we needed only 1 bromine tab in the floater when there was no use, in order to keep the bromine reading in range.  (I don't know if our service person used MPS then at all-should he have?) In summer, I figured we'd have to fill the floater full before each group comes. The only trial and error we can do is our guy will test before and after each group. Generally 5-6 people for 4 -6 nights. Unless maybe I asked him to come each day for the first group to check it. 

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The bromine three step method is usually recommended in the context of a private spa where the owner has complete control over the process. Your situation is a little bit more complicated. That being said, the three step method calls for the oxidizer to be added after each soak in the proper amount. There is therefore no need for a weekly dose of oxidizer. If the water chemistry is kept up properly, the water will always be clear and safe, without the need for additional weekly treatments.

During the winter when the spa was not being used, if your service person added MPS or some other oxidizer on a weekly basis, then the single tab in the floater was not the only thing keeping the bromine level up. You'd have to ask him.

During the summer, if you fill the floater full, then you will need less oxidizer after each soak, and during periods of no bathers, the bromine level will most likely increase.

Leisure time replenish is 15% dichlor and 85% other ingredients. They don't seem to publish what the other ingredients are, but basically, dichlor adds both chlorine and cyanuric acid to the water. In a bromine spa, the cyanuric acid would bind (buffer) some of the chlorine and prevent it from activating the bromine. the more you add, the more the cyanuric acid builds up, binding more chlorine. It seems to me it would be counterproductive.

There are various causes for cloudy water. The most likely cause in your situation is excessive bather waste, body oils, cosmetics, soap, and other foreign substances that has not been neutralized with sanitizer or oxidizer. The other danger from excessive bather load is that the sanitizer level goes down below the safe level, maybe even to zero. In that case, the water can become unsafe very quickly, and the cloudy water can potentially be the first indication of an algae bloom. In your commercial situation you should be particularly careful not to let that happen.

For bromine, some say the safe level is 4 to 6 ppm, some say 3 to 5 ppm. In my experience, I have found that even in my own very controlled situation - it's only me and my wife - that if I let the bromine stay around 3 to 5 ppm the water can get dull, or even cloudy. I have learned that at least in my own tub, I need to keep the bromine level higher than the usually recommended level of 4 to 6 ppm. We soak in the evening, I add oxidizer (I use bleach) after the soak, and then I test the following afternoon. I try to keep it so that the bromine is around 8 ppm plus or minus. This provides enough sanitizer to burn off any bather wastes, combined bromines, and other pollutants.

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Sorry, that was just a typing error on my part. I have corrected it above.

Replenish is Dichlor. Renew is MPS.

In my opinion, it is best to broadcast the chemicals onto the surface of the water. If you put chemicals in the filter compartment, they will go through the plumbing and heater and pump at much higher concentrations, possibly causing damage to the equipment.

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