Role of MPS after soak compared to Bleach?....just trying to understand this better


Well-known member
Jan 26, 2021
In a post on this forum by ChemGeek, he said....."If 3 people soak for an hour in a 350 gallon hot tub, then this requires about 7*3 = 21 ppm FC of chlorine or MPS equivalent. That's almost 11 teaspoons (almost 4 tablespoons) of Dichlor or 15 fluid ounces (almost 2 cups) of 6% Clorox Regular unscented bleach or 22 teaspoons (a little over 7 tablespoons) of MPS."

I'm trying to understand the role/function of MPS after a soak compared to adding bleach. Is adding this level of MPS (about 7.3 t. per soaking hour per person) after a soak pretty effective at leaving the tub at a similar FC level after the soak. I know that demand is different based on cleanliness of bathers but let's assume that bathers are using the estimate of about 7 PPM of FC per bather hour.


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TFP Guide
Oct 20, 2017
Southern WI
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Liquid Chlorine
MPS is an oxidizer but not a sanitizer. Chlorine is both an oxidizer and a sanitizer. Oxidizing is breaking down waste like sweat and skin oils. Sanitizing is making sure bacteria and the like can't grow. So basically MPS can be used to break down bather waste but you need some chlorine or bromine too as a sanitizer since MPS cannot do that job.

The advantage to MPS after a soak compared to adding bleach is that it can break down the waste without producing CC's. So if you are having an issue with CC buildup from using only chlorine, the use of MPS immediately after using the tub to break down bather waste can be an advantage here. However after the MPS has had a chance to break down waste you must add and maintain an adequate level of FC to ensure a sanitary hot tub.
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