In recent years, popular use of borates has increased due to users’ assertions that it can lower chlorine demand, help prevent algae, stabilize pH, increase the service life of pool equipment and improve the look and feel of the water. Those are a lot of bold claims. While chlorine is selling at a premium, now may be a good time to experiment and see if they live up to all the hype.
Preventing Algae/Lowering Chlorine Demand
Many claim that borates can help lower chlorine demand by preventing algae. They do this, not by actually killing algae, but by preventing its growth and reproduction. Borates are believed to disrupt cell division, which reduces replication. By minimizing algae growth, they are said to lower the chlorine demand.
According to a fact sheet from the EPA, boric acid was first registered as a pesticide in the U.S. in 1948. Currently, numerous pesticide products are registered which contain boric acid or one of its sodium salts as an active ingredient.
At the concentrations used in swimming pools, it is not easy to find evidence that borates truly function as algaestats. That said, thousands of borate users have reported that incorporating borates in swimming pools make them much less susceptible to algal blooms.
pH Stabilization/Increasing Service Life of Pool Equipment
Among the biggest advantages to using borates is its ability to stabilize the pH of swimming pool water. It is also the most complicated aspect to understand as it involves some complicated chemistry. A buffer is defined as a chemical system that resist changes in pH.
The chemistry is as follows: B(OH)3 + H2O ↔ B(OH)4- + H+ Boric acid reacts with water to form the borate ion and a hydrogen ion.
Although the borate buffer system buffers in both directions – both a rise and a fall in pH, it buffers better against a rise in pH. Using a borate buffer system allows pool operators to lower the total alkalinity a little and simultaneously control the rate of pH rise.
That makes it an especially useful tool in salt water chlorine generating swimming pools, which tend to experience pH drifts in an upward direction. Any changes in pH are buffered by the borates, which resist that change. This has the added benefit of reducing the rate of scale formation that tends to form on the salt water chlorine generator’s cell. As the current trichlor shortage may increase the installation of salt systems, borate use may be an especially useful trick for service techs.
Borates are also said to increase the service life of other equipment and fixtures. Users have reported that everything seems to last longer, from equipment to rails and ladders, and even vinyl liners.
Improved feel / Sparkly Water
Most users of borates report that the water feels silkier and has improved sheen. Some have attributed this observation to the possibility that borates reduce the surface tension of the water.
How to use Borates
The optimal concentration of borates in a swimming pool is 50 ppm. This is calculated as parts per million boron. Getting to that concentration of borates will depend on the type of borate starting material. For example, it can be added as boric acid, as borax, as a neutralized borate and as sodium tetraborate pentahydrate. In general, adding borates can be expensive. However, it is only really necessary to add borates once, unless the pool is drained, because borates don’t degrade or get used up.
Boric acid, which is available as a pesticide from hardware stores, is available in small quantities but larger amounts are available online. Adding boric acid to the pool is relatively cheap and easy, and it does not usually require a pH adjustment following treatment, which further lowers the cost.
The rule of thumb is that 4.75 pounds of boric acid will bring 10,000 gallons of water to 10 ppm.
The amount of borates desired is 50, therefore 23.75 pounds of boric acid will bring 10,000 gallons of water to 50 ppm.
Next, simply multiply 23.75 by the actual pool volume, and divide by 10,000.
For example, if the pool volume is 25,000 gallons, it would require 59 pounds of boric acid.
Nearly this quantity of boric acid can be found online, and is offered at prices from between $45 to $70 depending on whether it is purchased in bulk.
Borax, or sodium tetraborate decahydrate, is readily available in most grocery stores under the trade name 20 Mule Team Borax. During application, it is necessary to neutralize the pH rise that will occur upon addition of borax. It is sold in boxes that weigh 65 oz.
It takes 12 oz by weight of borax to raise 1,000 gallons by 10 ppm and requires 6 fluid oz. of acid to neutralize that pH rise.
Because 50 ppm is desired, 60 oz of borax is needed to raise 1,000 gallons to 50 ppm. For a 25,000-gallon pool then, 1,500 oz will be needed. Converting to the number of boxes needed, at 65 oz per box, it will be necessary to use 23 boxes of borax.
For the acid, it takes 6 fluid oz of muriatic acid to neutralize the pH rise of 12 oz of borax in 1,000 gallons. In the same 25,000-gallon pool requiring 1,500 oz of borax, it will require 750 fluid oz of muriatic acid. Converting to gallons, where there are 128 oz per gallon, it will take 5.9 gallons of acid.
Each box of borax costs about $4.50 at the dollar general. That’s $103.50 for the proper dose of borax for the hypothetical 25,000-gallon pool. Leslie’s sells muriatic acid for about $5.00 a gallon, so that is $29 in acid, bringing the total to $132 for the borate treatment of this pool.
1. Adjust the total alkalinity to between 70 and 80 ppm for salt pools or pools using hypochloritebased chlorine. For Trichlor, adjust alkalinity to about 100 ppm.
2. Adjust pH to between 7.4-7.6.
3. With the pump running, add half of the calculated acid add to the pool. Pour it slowly at the returns or dilute about 1/2 gallon at a time in a 5 gallon bucket of pool water and broadcast it around the pool. As soon as the acid is in put in 1/2 the borax.
4. Brush down the sides of the pool all the way around. The goal is to thoroughly mix the solution.
5. When brushing is complete, add the rest of the acid and the rest of the borax and brush again.
6. Allow the pump to run for 24-48 hours.
7. After 48 hours, test the borates and pH. It may be necessary to add more acid to bring the pH down.
8. Test the borate levels monthly. If the filter is frequently backwashed, it may be necessary to test a bit more often. When the borates drop to about 30 ppm increase them another 20 ppm to bring them back up to 50 ppm by adding the acid and borax.
Sodium Tetraborate Pentahydrate
Sodium tetraborate pentahydrate is added to the water in a manner similar to that of borax. However, because it has half as much water as the decahydrate form, less will be required.
It requires 5.6 pounds of sodium tetraborate pentahydrate to bring 10,000 gallons of water to 10 ppm, and 10 oz of muriatic acid to neutralize every 1 pound of sodium tetraborate pentahydrate.
It takes 28 pounds of sodium tetraborate pentahydrate to raise 10,000 gallons to 50 ppm. For a 25,000-gallon pool, that works out to 70 pounds. Because 10 oz of muriatic acid neutralizes 1 pound, 700 fl. oz or 5.46 gallons of muriatic acid will be required to neutralize 70 pounds of borates.
Today, sodium tetraborate pentahydrate costs $50 for 20 pounds, or $2.50 a pound, and a 25,000-gallon pool needs 70 pounds, bringing the total to $175 in borates. Meanwhile, muriatic acid costs about $5 a gallon, and we need 5 ½ gallons, bringing the cost of muriatic acid to $27.50. To treat this pool, it will cost a grand total of $202.50.
It is possible to purchase borate products that contain pH neutralizing chemicals making it unnecessary to add muriatic acid after treatment. One manufacturer sells 45 pounds of neutralized borates on Amazon for $265.
That works out to $5.88 a pound. The directions say to use 2 pounds per 1,000 gallons. So, for a 25,000-gallon pool, that’s 50 pounds of borates. At $5.88 a pound, it would cost $294 to dose the pool.