Pool Sanitizers, Part 2: Chlorine Alternatives
In part 1, we discussed the various types of chlorine, and why a residual pool sanitizer is essential for a safe, healthy swimming pool. This article will cover chlorine alternatives. Again, this is taking a vast array of information and simplifying it for you to read... as always, if you want to learn more, we encourage you to research these topics further.
- Byproducts in pool water: hypobromous acid (HOBr) + hydrobromic acid (HBr)
- pH: Bromine is 3.8-4.0 (strongly acidic), and Sodium Bromide is between 6.5 and 8.0.
Pool operators can introduce bromine as sodium bromide (bromine "salt"), with the addition of another oxidizer like ozone. This is most commonly used as a bromine shock or an algaecide in a chlorine pool. There are problems with that, as outlined below. People use bromine tablets more commonly. They can be added to a floater or an inline bromine feeder, similar to a cal hypo feeder. Like chlorine, bromine will not disinfect until the oxidant demand has been destroyed.
Pros: Bromine in swimming pools behaves differently than chlorine in a few ways. First, unlike chlorine, bromine can be recycled. After the oxidation process, it can regroup its byproducts (such as bromides) with a separate oxidizer (like ozone or potassium monopersulfate) to re-form hypobromous acid, the killing form of bromine. In fact, bromine kills only after being converted into hypobromous acid (HOBr) first. Hypobromous acid is very effective against algae and germs, and works in a wide range of pH, unlike chlorine.
Cons: There is no stabilizer like cyanuric acid for bromine. It breaks down in direct sunlight quickly, forming a byproduct the EPA considers carcinogenic: bromate ion. Therefore, bromine is not an appropriate product to be used in outdoor pools. In fact, the NSF has determined that any bromate ion level exceeding 3.3 parts-per-billion is unsafe for drinking water (NSF/ANSI Standard 60). Apart from bromate ions, using a little bromine in a chlorine pool turns it into a bromine pool over time. "Once a bromine pool, always a bromine pool."
Warning: Never add cyanuric acid to a bromine pool. Hot tub and spa covers block sunlight from turning bromine into the harmful bromate ion; a benefit to spa owners.
Bromine can also sanitize and disinfect, as well as oxidize. It's just weaker than chlorine in those efforts.
2. Potassium Monopersulfate
- Byproducts in pool water: Nitrate ions, sulfate, and...well it's complicated...Read this for details.
- pH: 2.1 (extremely acidic)
Pool professionals use potassium monopersulfate (KMPS or MPS) as a non-chlorine shock. It is compatible with chlorine pools and bromine pools, but not cost effective for long-term use. That's why it is primarily used in small bodies of water, like hot tubs and spas. It is an oxidizer, but not a sanitizer, so it cannot be used to replace chlorine.
Pros: KMPS boosts sanitizer efficiency because it helps oxidize contaminants. In that sense, using KMPS as a shock is another way to remove organic waste.
Cons: Potassium monopersulfate will give some test kits a false reading for combined chlorine, due to how it reacts with their reagents. KMPS is one of the more expensive chlorine alternatives. It is primarily used as a non-chlorine shock, since it is not even a sanitizer (it is just an oxidizer). One byproduct of oxidizing bather waste with KMPS is the nitrate ion, which is very hard to remove from pool water. KMPS is also very acidic, which will lower pH and alkalinity.
Contrary to popular belief, however, potassium monopersulfate does not eliminate chloramines. That bears repeating: potassium monopersulfate does not eliminate chloramines.
As far as chlorine alternatives go, biguanide is a sanitizer, but not an oxidizer.
Pros: Generally regarded as safe to handle, and lasts longer in the water than chlorine or bromine. The perception of having a "chlorine free pool" is appealing to many homeowners, and using biguanide as the primary pool sanitizer can accomplish that. Biguanide is also gentle on skin, pool liners and bathing suits.
Cons: Biguanide products sanitize less efficiently than chlorine, given that it takes 30+ parts-per-million to sanitize water (compare that with 1.0-3.0 ppm chlorine). Biguanides are also expensive products, and since they do not oxidize, removing bather waste from the water remains a problem. Most debris flocs and is captured through filtration...which leads to clogged filters over time. With every action there is a consequence. Another con of biguanides is that they are incompatible with chlorine, so in order to have oxidation, you must use something like potassium monopersulfate.
Many residential pools use dissolved metals as a sanitizer. Usually it is silver or copper, and these metals can be effective at what they claim. Copper-based algaecides, for example, are very effective at killing algae. The question we have at Orenda is this: once the metals are in the water, how do you get them out?
At a certain point, dissolved metals can be harmful to people, especially if accidentally consumed (yes, people accidentally swallow pool water). The industry claims a difference between "chelated metals" and "non-chelated metals". But even when using a metal control product, metals can still over-saturate and cause problems.
We at Orenda are not proponents of using any heavy metals as chlorine alternatives in pools...even though they are effective sanitizers. We already have to deal with metals in the source water, so deliberately adding more to the pool just compounds the issue and leads to more problems (like stains). But more importantly, they stay in the water for a long, long time.
Conclusions about chlorine alternatives
These articles are meant to inform, not lecture. While we share our opinions, we are always paying attention to how these technologies develop over time. We encourage you to do the same to make the best decisions for your pool, and/or your customer's pool.