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Why Do I Need to Use Hydrogen Peroxide in My Hot Tub?

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Earlier today we heard from 'Vick' who asked, "We just got a hot tub and the salesman said to use a biguanide system that also uses hydrogen peroxide.  Why do we need to use two chemicals?  Why doesn't the biguanide stuff do the job all on its own?  So we HAVE to use the peroxide or is that just another selling trick to make us buy more chemicals than we really need?"

Thank you for the question, Vick, and congratulations on the hot tub purchase!

Why do you need to use a second chemical (such as peroxide in this case) with the biguanide chemical to keep your water safe/clean?  Although the Environmental Protection Agency HAS approved Polyhexamethylene biguanide (PHMB), more commonly referred to as just biguanide, as a disinfectant for microbiological control, biguanides do not have the ability to oxidize organics.  Therefore a second chemical must get used to oxidize organics in pool and hot tub water.

OK, so why not use chlorine or bromine?  In a nutshell, both chlorine and bromine react VERY badly with biguanides and in extreme cases chlorine and bromine will cause the biguanides to come out of solution (become 'solid' and visible in the water).  Hydrogen peroxide, on the other hand, packs a powerful oxidizing punch and does not have chemical compatibility issues with biguanides.

While on the topic of biguanides and chemical compatibility, in addition to chlorine and bromine, biguanides also do not play well with copper agaecides and non-chlorine 'shocks' that contain monopersulfate (MPS).

Testing for peroxide in water

Can the average person test for peroxides in their water?  Yes.  The WaterWorks Peroxide Check (MPN 480014) product detects up to 100ppm (parts per million) peroxide in water and the test takes just a few minutes to perform.  This simple dip and read testing product has color blocks at the following levels:  0.05, 2.0, 5.0, 10, 25, 50, 100 ppm.

Peroxide in Water Test
Peroxide in Water Test
Water Metals Test Strips
Water Metals Test Strips
John's Total Copper in Water Test
Total Copper in Water Test