# Thread: 43% MPS vs 72% MPS - chemgeek?

1. ## 43% MPS vs 72% MPS - chemgeek?

Not sure if anyone knows the answer to this but I was reading some old posts and saw where chemgeek said that for 43% MPS you need 7 teaspoons per person-hour (assuming no ozonator). That's less if you have Nature2 right?

Assuming tho no Nature2, what is that with 72% MPS? I just found out that's what my leisure time Replenish is, 72% MPS, 15% di-chlor and the rest "other". Is it straight math of (43/72)*7? So ~4.2 teaspoons / person hour? And I guess with the 15% di-chlor that would be even less, but let's just ignore the di-chlor for arguement's sake.

thanks!

2. ## Re: 43% MPS vs 72% MPS - chemgeek?

It's not less with Nature2 since that is just silver ions and they do not oxidize bather waste.

Replenish is not actually 72% MPS (see this MSDS and this link). It's 72% of the triple salt that if it were the usual product would be 43% potassium monopersulfate (MPS), 23% potassium bisulfate, 29% potassium sulfate, 3% potassium peroxydisulfate, and 2% magnesium carbonate. So the Replenish is actually 0.72*43% = 31% MPS. In general it's best not to use combination products, but if you want to use this then one teaspoon of it is the same as 0.72 teaspoons of the pure triple salt (43% MPS) and 0.15 teaspoons of Dichlor so would handle 0.72/7 + 0.15/3.5 = 0.146 person-hours so 1/0.146 = 6.9 teaspoons (about 7 teaspoons) would handle one person-hour. So basically it's similar to being an MPS product in terms of the amount that you use though it has some Dichlor so will be adding some chlorine and CYA.

3. ## Re: 43% MPS vs 72% MPS - chemgeek?

Ah ok, I had seen the poolgeek link but I was reading that as a strength for some reason vs the amount of total product. So for our 2 person 40 minute soak (1.33 person hours), we really should be adding in 10tsp vs the 6 or so we've been adding. Interesting. We started with this stuff because that's what the pool store gave us but perhaps when it's done we'll switch to something that's just MPS. Do the other products in it (i.e. the potassium types and the mag carb) do anything overly useful? Claims to be a buffer and clarifier too as well as oxidizer. Water is super clear and the pH isn't bouncing around. It's interesting how it says it uses Oxone to avoid adding any chlorine to your pool but with the 15% dichlor that seems like bad advertising.

4. ## Re: 43% MPS vs 72% MPS - chemgeek?

Yes, the poolgeek ingredients list is a bit misleading. The 72% is really for Oxone which is the triple salt with the percentages I listed. If you were to use MPS alone (with silver ions in the water, of course), then you may find you need to use chlorine once a week or so to keep the water clear. MPS doesn't oxidize everything chlorine does (and vice versa), but generally speaking chlorine does better than MPS, bromine, or even ozone at oxidizing bather waste to the point where the water remains clear. The main advantage of using MPS or ozone is that they oxidize bather waste without creating chlorinated disinfection by-products. So using a combination works well, but it doesn't have to literally be in a combination product.

The pH buffer that they may add just has the product be less acidic because MPS is acidic. If the buffer contains more carbonate, then it attempts to keep the TA more stable. If you use an MPS product you can just add baking soda to increase the TA as needed. It takes roughly 35% of baking soda by volume compared to the pure Oxone products (43% MPS) to keep the TA constant so 2-1/2 teaspoons of baking soda for every 7 teaspoons of MPS which corresponds to one person-hour of soaking. In 350 gallons the 7 teaspoons of MPS product by itself would drop the TA by 6.3 ppm.

5. ## Re: 43% MPS vs 72% MPS - chemgeek?

Chemgeek - can I reopen this one too for a minute? Knowing that I want to use up this replenish with the ingredients from the posts above, do you know how much each quantity of it (say 1 tsp or 1 tbsp) raises the CYA? So I know that dichlor for each 10ppm raises CYA 9ppm, but I don't have that type of number for my MPS (plus other "stuff") and given how you test CYA with 7ml of the reagent each time, I was hoping to avoid testing all the time to see what I'm at.

I know you said one teaspoon of it is the same as 0.72 teaspoons of the pure triple salt (43% MPS) and 0.15 teaspoons of Dichlor so I guess I could see what quantity of dichlor would raise the FC 10ppm in 500 gallons of water and then if it's say 1.5 tsp, then .15 teaspoons could be 1ppm FC and 0.9ppm CYA but then I don't know what the 0.72tsp of MPS does to my CYA. If that all makes sense of what I'm trying to get to.

6. ## Re: 43% MPS vs 72% MPS - chemgeek?

The MPS does nothing to your CYA. The CYA only comes from the Dichlor portion. Since that is 15% by weight of the product then if I assume a product density (from their MSDS) of 1.2 g/ml then 1 teaspoon is around 5.9 grams so using 15% of this for Dichlor in 500 gallons this is only 0.26 ppm FC and 0.24 ppm CYA.

7. ## Re: 43% MPS vs 72% MPS - chemgeek?

Thanks! At least now I can keep track without having to test all the time since with the nature2 and replenish I'm not as concerned with my fc number until I change over to bleach but want to switch over much earlier than I did last fill.

8. ## Re: 43% MPS vs 72% MPS - chemgeek?

Looks like their product density is off. Going off 3tsp = 1tblsp, we weighed out 1 tablespoon of the Replenish and it's 27g. So 15% of that is 4.05g which in 500 gallons (or 1,893 liters) will raise the FC 1.2ppm and the CYA will go up 1.1ppm if I did all that math correctly and can read pool math

Interesting the weights are so different from the MSDS sheet. We used a kitchen scale vs my gun powder scale. Wonder if that'd be more exact and closer to published numbers. Might try that when I have time.

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