What is Biguanide?

For those looking at chlorine-alternatives, the options may be confusing. Do you go with ozone? Bromine? Biguanide? That last one may be unfamiliar to many pool owners, so we’ll explain the pros, cons, and usage instruction for the latter form of sanitizer.

What is biguanide?

Otherwise known as polyhexamethylene biguanide (PHMB), biguanide is a complete alternative to chlorine/bromine products that will NOT work with other kinds of sanitizing systems. Unlike some other sanitizers that are chlorine compatible, if you decide to go with biguanide you must make a 100% switch since it’s based on entirely different chemistry than bromine or chlorine.


Biguanide is an effective microbe killer. It was originally used in gauze dressings on wounds and contact lens solutions because it’s so good at preventing bacterial growths that would result in infections. It works by attracting bacteria into it, penetrating the cell wall of any unwanted germs, and breaking down and killing the bacterium.

Used to kill bacteria for more than 20 years, it was initially registered with the EPA as a sanitizer. One of its main benefits is the fact that it does not break down in the sunlight or in high temperatures, meaning its effectiveness is maintained. Some products (like bromine) need to be replenished more often because the sunlight decreases its strength/effectiveness.

It also doesn’t have some of the less-than-desirable affects that sometimes accompanies chlorine like the smell and the eroding effect on vinyl liners or bathing suits. Owners with biguanide pools also report their water feels softer and smoother than their chlorine sanitized water.

Switching to Biguanide

When switching from regular sanitizers like chlorine, you won’t have to empty your swimming pool in order to change the sanitizer. Expect one or two days for the biguanide to kick in after you’ve started the process.

First, take a sample of your water and evaluate it for metals which can cause staining during this process. If you’re not sure what to look for, contact your local pool professional.  To begin, add a reducing agent to the water to eliminate the chlorine or bromine. Run the pool for another 8-12 hours then check the sanitizer level, adding more neutralizer if needed. DO NOT add the biguanide until the level hits zero.

If you’re switching to biguanide in your hot tub, the simplest course of action is to drain your tub, wash it out, and start off with fresh water.

Maintaining a Biguanide System

If you’re buying biguanide products, it’s best to stay within the same product family to make sure they all work together seamlessly. You should check your biguanide levels weekly. Avoid using traditional test strips as they don’t always yield accurate results. Use a specialized strips that are biguanide specific or purchase a test kit that is biguanide compatible. Add more biguanide to the water when the test has results lower than 30 ppm.

Because you can’t perform a standard chlorine shock, biguanide pool users will need to shock their pools with hydrogen peroxide to get rid of any organic build up. Swimmers will need to stay out of the pool for only about 15 minutes after a hydrogen peroxide shock.


Despite the benefits of a biguanide system, there are some complications that come along with it that owners should be aware of.

If the water becomes cloudy in a biguanide pool or spa, it’s usually because the possible slime and mold problem that goes along with the system forces owners to use biguanide products at a higher rate or the oxidizer will get used up. This often turns water cloudy.

Biguanide users should also backwash their filter in a spa and use a filter-cleaning product monthly because of the gunk build-up associated with it that isn’t as easily eliminated like with chlorine treated water. Biguanide cannot destroy organic contaminants which is why hydrogen peroxide is needed for shocking the system.

The cost is a major deterrent for many considering the switch. Compared to traditional sanitizing systems, it often requires more product at a steeper price.

Although there is little to no chemical odor, biguanide does cause a lot of foaming. It is a problem that usually needs to be monitored on a daily basis.

Perhaps the biggest issue is that after several years, sometimes biguanide-resistant microorganisms develop in the water. It takes the (super unpleasant) form of pink slime or water mold. The only way to treat it is to apply large amounts of chlorine and/or chlorine shock which will destroy all the biguanide in the water.

So what do you think - is it worth it to make the switch? Does anyone have a biguanide pool system that they love? Comment below!

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