When it comes to pool and hot tub sanitizers, chlorine and bromine aren’t the only chemicals in the conversation.
In this article, we’ll cover what biguanide (Bacquacil) is, the benefits of using it, and how it stacks up against conventional sanitizers.
Quick answer: Biguanide is a chlorine alternative that’s notably less harsh on the body, but its higher cost and inability to break down non-living contaminants make it difficult to justify over chlorine in most cases.
What Is Biguanide?
Polyhexamethylene biguanide (PHMB), often just called biguanide, is a popular chlorine alternative for pool and hot tub sanitation.
It’s also known as brand names Baquacil, SoftSwim, Revacil, and Aqua Silk.
Despite being a sanitizer, it works a little differently from chlorine. Where chlorine penetrates microorganisms and disrupts the inside of the cell, biguanide instead focuses on (and binds to) the cell wall.
Essentially, chlorine works from the inside out and biguanide works from the outside in.
Why Use Biguanide Instead of Chlorine?
There’s a lot to like about Biguanide as a primary pool sanitizer, even when stacked up against almighty chlorine.
Here are the main benefits:
It’s Gentler on the Body
Biguanide is much gentler on the body, especially for those who are highly sensitive or allergic to chlorine.
Compared to chlorine and even its softer cousin, bromine, biguanide causes little to no irritation to your skin, eyes, and hair.
This is because biguanide doesn’t react with non-living contaminants, meaning it doesn’t attack the proteins in our bodies (yes, they’re considered non-living) that would otherwise lead to redness and itchiness.
Chlorine and bromine also form chloramine and bromamine when they get used up in the water. These byproducts lead to further irritation and a pungent smell that causes respiratory issues at higher concentrations.
Since biguanide doesn’t contain chlorine or bromine, those nasty byproducts aren’t formed during the sanitation process.
It Stays in the Water Longer
A big part of this has to do with sunlight.
Chlorine is quickly broken down by UV light and is often paired with cyanuric acid (a chlorine stabilizer) to shield it from this effect. Bromine is naturally more resistant to UV than chlorine but it can’t be stabilized.
Biguanide puts both sanitizers to shame here. Not only is it considerably more resistant than chlorine and bromine, it also doesn’t require any stabilizer.
It’s also worth mentioning that biguanide isn’t an oxidizer like chlorine and bromine, so it doesn’t “gas off” when it reacts with certain contaminants in the water.
Instead, used-up biguanide stays in the water until it’s removed through filtration — though it provides no extra benefit in terms of sanitation.
It Doesn’t Impact Your pH Level
Biguanide is pH neutral; so it won’t change the pH level of your water.
This is helpful in maintaining the balance of your pool as you don’t need to worry about pH corrections whenever you’re adding sanitizer.
With a chlorine or bromine pool, you always need to be conscious of this because chlorine will usually raise or lower the pH level of the water depending on the form of chlorine used.
For example, most tablets are highly acidic and will lower pH, while some types of granular chlorine are highly basic and will raise your pH. Bromine tablets are also slightly acidic and will lower your pH over time.
So… What’s the Catch?
Chlorine didn’t become the most dominant pool sanitizer by accident; it’s incredibly convenient, highly effective, and relatively cheap.
Biguanide doesn’t quite check the same boxes.
It Doesn’t Work on Everything
Remember, biguanide is a sanitizer but not an oxidizer.
That means it’s very capable of killing most living microorganisms found in a pool, including bacteria, viruses, and most types of algae — but it can’t break down non-living contaminants.
Without an oxidizer, things like sweat, body oils, urine, cosmetics, and sunscreen will continue to build up in your pool until it becomes cloudy, dirty, and unsafe to swim. This can also provide a food source for biofilm-forming organisms like white water mold and pink slime.
The good news is, biguanide can be paired with hydrogen peroxide (an oxidizer), but it needs to be carefully balanced alongside your biguanide level to ensure it doesn’t get too high or too low.
While biguanide is a viable alternative to chlorine and bromine, it requires a bit more work to manage because it relies so heavily on an additional chemical.
Note: You should never use non-chlorine shock (MPS) in place of hydrogen peroxide. Even though it’s an oxidizer, it reacts badly when paired with biguanide.
It’s Considerably More Expensive
Biguanide is considered somewhat of a “specialty sanitizer” so it tends to be pricier than what you’d expect from other pool sanitizers.
Even with the recent price increases on chlorine, it’s still relatively inexpensive and you will likely spend multiple times that amount when switching to biguanide.
You also have to factor in the added cost of hydrogen peroxide when using biguanide, as it needs to be paired with an oxidizer.
Hydrogen peroxide isn’t necessarily expensive but it’s still an unwelcome expense given the already higher cost of biguanide.
Finally, there’s an indirect cost as a result of higher testing frequency. Since both biguanide and hydrogen peroxide needs to be kept balanced, you may have to test more frequently than if you were just using chlorine.
Should You Switch to Biguanide?
Well, probably not.
For most pool owners, chlorine is still king. It’s the most effective, convenient, and inexpensive pool sanitizer on the market, and for the majority of swimmers, the side effects are mild and easy to overlook.
When you consider that most chlorine comes pre-stabilized (to protect against UV) and the pH impact on your water is slow, the added benefits of biguanide quickly become irrelevant.
Overall, given the additional cost and complexity of using biguanide over chlorine, it’s simply not worth it for the majority of people.
With that said, for the small percentage of people who are significantly impacted by chlorine and have no choice but to seek an alternative, biguanide is very viable if you’re willing to make those concessions.
Note: Chlorine and bromine don’t play nicely with biguanide. You’ll need to fully drain your pool and start fresh if you plan on making the switch.
The Bottom Line
Biguanide (or Bacquacil) isn’t necessarily better than chlorine or bromine, it’s just a different kind of sanitizer with different benefits and drawbacks.
If you’re highly sensitive to traditional sanitizers and are willing to pay a premium, biguanide might be the obvious choice. If cost-effectiveness and convenience are your top priorities, chlorine still reigns supreme.
