Borates: the buffer most pools never add

What borates actually do

Two things, according to published pool chemistry. Orenda describes the pH mechanism as boric acid buffering against increasing pH by taking or giving away a hydroxide ion, and the algae mechanism as borates disrupting cell wall development, metabolism and cell division.

The pH effect is the one that matters most in practice. A pool with high alkalinity or an aerated water feature has pH that climbs no matter what you do, and our high alkalinity guide covers why chasing it with acid is a treadmill. Borates do not replace correct alkalinity; they resist the drift on top of it.

The algae effect is real but modest, and the word to hold on to is algaestatic rather than algaecidal. Borates make it harder for algae to establish. They will not clear an existing bloom, which is a job for the process in our algae guide.

AquaChek, which makes the test strips, summarizes the whole case as borate working as a buffer to help control pH, aid in algae prevention and contribute to water clarity and a softer feel of the water.

The range, and the ceiling

Orenda publishes that borates are most effective between 30 and 50 ppm, and that 50 ppm is the maximum level in a pool. AquaChek’s strips read 0 to 80 ppm, which covers the working range with headroom to tell you when you have gone too far.

There is no way to know where you are without testing, because borate does not appear on any standard multi-way strip. That is the single most important practical point on this page: if you are going to run borates, you need the dedicated strips, or you are dosing an invisible parameter by arithmetic alone and hoping.

The product question, answered honestly

There are three chemical routes published by Orenda: borax, which is sodium tetraborate decahydrate; sodium tetraborate pentahydrate; and boric acid. The tetraborate forms raise pH as they dissolve and therefore need acid added alongside them to bring pH back; boric acid does not.

The widely repeated home method uses laundry borax with muriatic acid to correct the pH rise. Here is the caveat that most pool articles omit: 20 Mule Team publishes its product as sodium tetraborate and lists its uses as cleaning, laundry, odor control and crafting. Swimming pools appear nowhere on its site. It is not sold, labeled or approved as a pool chemical, and we are not going to link a laundry product as one.

Orenda’s own framing on this is worth repeating: products used in recreational water should be EPA registered, NSF-50 or NSF-60 certified. That is the standard a purpose-made pool borate product meets and a box of laundry booster does not. If you use the borax route — and many experienced pool owners do — you are making an informed off-label choice, not following a manufacturer instruction, and the acid handling that goes with it is the genuinely hazardous part.

Who should bother, and who should not

Worth considering if your pH climbs relentlessly despite correct alkalinity, if you run a salt system — salt cells drive pH up as a matter of course — or if you have an aerated feature. Our pH and alkalinity guide covers the diagnosis that tells you whether this is your pool.

Not worth it for the average seasonal frame pool. A 3,000 gallon pool that is emptied at the end of summer gets most of the benefit from simply testing weekly, and the money is better spent on a cover. Borates are an addition to a well-run pool, not a substitute for running it well.

Skip entirely if you are not going to test. An untested borate level is an unknown you have introduced deliberately, and the ceiling exists for a reason.

If you do add them

1. 1

   Fix alkalinity first

   Borates buffer on top of carbonate alkalinity; they do not replace it. A pool with alkalinity out of range should be corrected before anything is added.
2. 2

   Work out the dose from your real volume

   Dosing is per gallon, so the number has to be right. Our sizing guide covers working out an honest volume rather than the number on the box.
3. 3

   Add gradually, and test as you go

   Aim for the lower end of 30 to 50 ppm first. There is no practical way to remove borates except dilution, so undershooting is the recoverable error.
4. 4

   Correct pH afterwards if you used a tetraborate

   Borax raises pH as it dissolves. Acid handling is the dangerous step here - eye protection, never into a confined space, never mixed with anything else.
5. 5

   Retest monthly

   Borate is not on general test strips, so it needs its own. Levels fall as water is splashed out and replaced.

Used this way, borates are a quiet improvement to a pool that already runs well: steadier pH, slightly less chlorine demand from nuisance algae, and water that feels softer. They are not a chlorine alternative, which is a separate and much-oversold category covered in our chlorine alternatives comparison.

What borates will not do

Three claims circulate about borates that are worth separating from the two published mechanisms.

They are not a sanitizer. A borate pool still needs chlorine at the levels health authorities publish — CDC guidance for home pools is at least 1 ppm free chlorine, or at least 2 ppm where a stabilizer is in use, with pH between 7.0 and 7.8.

They are not an algaecide. Algaestatic means algae find it harder to establish, not that an existing bloom clears. Our algaecide roundup covers the products that do that job, and the honest framing there is the same: insurance rather than rescue.

They do not replace alkalinity. Carbonate alkalinity is still the primary buffer, and a pool with alkalinity out of range does not become stable because borates were added on top. Our alkalinity guide is the prerequisite.

There is also a regulatory wrinkle worth knowing if you are comparing branded products. One well-known pool borate product was previously sold as an EPA-registered algistat, and its current version is not an EPA-registered product. That does not make it ineffective as a buffer, but it does mean claims about algae on the box and claims on a registration are two different things.