Borates stabilize pH, reduce algae growth
When it comes to pH buffering systems in swimming pools, the carbonate system is king, but there are additional pH buffers that are also added to pools that can provide additional benefits, and one such buffer is borate.
Buffers are molecular species that resist drastic changes in pH. One definition of pH is that it is a measure of the concentration of hydrogen ions in solution. A large concentration of hydrogen ions corresponds to a low pH, whereas a small concentration of hydrogen ions corresponds to a high pH. Buffers resist drastic changes in pH by either releasing or consuming hydrogen ions. Depending on the pH of a solution, they can either release hydrogen ions in the water, or combine with hydrogen ions in the water to remove them from the solution.
The practical pH range of a buffer is one pH unit above or below the optimum pH. In swimming pools, the carbonate buffering system is most effective at resisting pH fluctuations at a general pH of 6.3. In most swimming pools, cyanuric acid also serves as a buffer system. While most operators don’t add it for that reason, it is maximally effective at the useful pH of 6.8.
By contrast, maximum buffering in the boric acid/borate system occurs at pH 9.2; at and above pH 7.8, borates can significantly supplement swimming pool buffering.
Like all buffers, borates resist changes in pH when either an acid or a base is added. Thus, they can mitigate against large drops in pH when acidic sources of chlorine are used, such as chlorine gas and trichlor, but they also resist increases in pH when basic sources of chlorine are used, such as sodium and calcium hypochlorite as well as when soda ash or sodium carbonate is added.
In addition to being useful as a pH buffer, many have noted that borates can improve both the look and feel of swimming pool water.
Richard Falk, a pool chemistry expert, believes that water may sparkle more in the presence of borates due to decreased surface tension, although he is the first to admit that the surface tension aspect has not been measured. He has speculated about this effect while conducting chemical tests in a test tube, and noticed a definitively flattened meniscus.
“I presume the effects are due to surface tension. The ‘sparkle’ is referring more to light reflection from the water surface especially when there are some small waves in the pool,” Falk wrote on the online forum, Troublefreepool.
Other users have speculated about decreased surface tension. Wasps that were once able to land on the water surface to drink the pool water were no longer able to after borates were added. The wasps drown, ending up in the skimmer.
Surface tension may also be a factor in the improved feel of the water. Users of borates have said the water feels “wetter,” “silkier” and “slick.”
However, scientific analysis of borate’s effect on surface tension apparently have not been published, so these reports are anecdotal.
Another benefit to using borates is that they can help reduce algae. Borate is a known algestat, meaning that it prevents algae growth. There are several published studies that have demonstrated this.
For example, in U.S. Pat. No. 4,594,091, issued Jun. 10, 1986 to John W. Girvan, a method of controlling algal and fungal growth using sodium tetraborate in water is described. At borate concentrations greater than 25 ppm, the author noted complete inhibition of Chlorococcum, an algae that is found in swimming pools.
Falk said that he has noticed algae reduction while using borates.
“I know from my own pool that 50 ppm borates with zero chlorine in the pool will NOT prevent all algae growth, in spite of what the patent says, but it DOES slow it down significantly even when I had greater than 3000 ppb phosphates. I would say it cuts down the growth roughly in the same amount as going to less than 500 ppb phosphates does, but that's just a rough guess based on what I've seen,” Falk said.
Because of these claims, some have stated that using borates can significantly reduce chlorine consumption.
Water chemistry consultant and author Bob Lowry has written that the use of borates can reduce chlorine consumption by 30% to 50%. This was a claim also made by Jim Halley, chemist for ProTeam, maker of sodium tetraborate pentahydrate.
However, not everyone agrees with this. Kim Skinner, member of the water chemistry consultants onBalance, believes the reduction in chlorine consumption is being overstated.
“Adding borate will NOT reduce chlorine costs by 30% to 50% as is being claimed. It is generally known that residential pools lose, on average, about 1 to 2 ppm of chlorine per day. According to many service companies, residential pools generally lose the same amount of chlorine daily whether they contain borate or not. And the suggestion to maintain lower chlorine levels when using borate is risky and problematic,” Skinner said.
However, Lowry says that it is logical to assume that there would be some reduction in chlorine use, because borates do prevent and may even kill some algae.
“I have never said that anyone should keep a residual less than recommended. However, there are two recommendations. Trouble Free Pools, Richard Falk, Ben Powell, et al. have been recommending a minimum free chlorine level of 7.5% of CYA without borate and 5% of CYA with borate at 50 ppm since ~2007. I have been recommending the same level since 2012,” Lowry said.
If the chlorine can be dropped from 7.5% to 5% in the presence of borates, that corresponds to a 33% reduction. Skinner says this is a theoretical assumption, but it doesn’t match real world experience.
Borates may or may not lower chlorine consumption.
Nevertheless, they provide additional buffering, reduce algae and improve the water’s appearance and feel.
Experts agree on this: borates make the water better.