Borates in a Pool: What They Actually Do (and What They Don't)

Borates are the closest thing pool chemistry has to a quiet advantage — and they are still not a miracle. Held at 30–50 ppm they buffer pH so it stops marching upward, they make it harder for algae to get going, and unlike almost everything else you put in a pool, they stay there. What they do not do is sanitize, and no amount of borate makes up for a filter nobody cleans.

What borates actually are

Borates are what you get when you dissolve a borate compound — borax (sodium tetraborate, the laundry box) or boric acid — into pool water. They form a buffer system that works alongside your total alkalinity.

That word “buffer” is the whole point. Pool pH almost always drifts up, because pool water holds more dissolved carbon dioxide than the air above it, and as that CO₂ outgasses the pH climbs toward a natural resting point around 8.2. Anything that agitates the surface — a waterfall, spa jets, aimed returns, a salt cell — speeds it up. Your total alkalinity is the primary brake on that climb. Borates are a second brake, working in a slightly different pH range, and the two together hold the line better than alkalinity alone.

The three things they genuinely do

1. They slow the pH climb, so you dose acid less OFTEN — not less. This is the effect with the clearest chemistry behind it, and it is also the one most often oversold, including by us in an earlier version of this page. Trouble Free Pool states the limit plainly: borates require the same amount of acid to manage pH, and what they reduce is the frequency of additions. The reason is that pH rise comes from carbonate alkalinity outgassing CO₂, and borates do not touch carbonate alkalinity. So the jug does not last longer over a season. What changes is that pH holds steadier between tests and you stop chasing it weekly — which on a pool with a salt cell or a water feature is a real quality-of-life difference, just not a cheaper one.

2. They buffer the pH spike inside a salt cell, which is where the scale comes from. This is the benefit TFP now leads with, and it is the most concrete one. An SWG is pH-neutral in the pool overall, but right at the plates the cell drives the local pH sharply up, and high local pH is what precipitates calcium carbonate onto the cell. Boric acid mops up the hydroxide the cathode produces (B(OH)₃ + OH⁻ ⇌ B(OH)₄⁻) before it can turn bicarbonate into carbonate, so less scale forms on the plates and the cell stays efficient longer. If you run salt, this is the reason to be reading this page.

3. They persist. Chlorine is consumed. CYA degrades slowly. Borates do neither. Nothing in normal pool operation uses them up, so once you are at 50 ppm you stay at 50 ppm until water physically leaves the pool — backwashing, splash-out, an overflow, a partial drain, or a leak. That is an unusual property in pool chemistry and it is most of why people who run borates keep running them.

There is also a fourth, softer benefit that is nearly universal in owner reports and that we will label as exactly what it is: swimmers describe borate water as softer on the skin, and the water often looks more sparkling. That is subjective. It is also reported so consistently that it is worth mentioning honestly rather than pretending it isn’t part of why people like it.

The algae claim, which we had too high

Borates are routinely described as algaestatic — suppressing how fast algae multiply without killing an established bloom. We published that as one of the three things borates genuinely do. Trouble Free Pool’s own wiki now says the effect is overstated at normal pool levels, and the numbers are not close.

Their reading: algae are low-sensitivity organisms needing somewhere around 10–24 ppm of elemental boron before growth is meaningfully inhibited, and a pool held at 30–50 ppm borates sits well below that. TFP’s conclusion is blunt — borates “only become truly algaestatic at concentrations above 100 ppm (and closer to 200 ppm)”, a level they describe as unsafe to swim in. Kim Skinner, whose service company has run borates since the 1960s, says the same thing from the other direction: it is “misleading to suggest that borates will eliminate or prevent algae.”

So treat any algae benefit as a bonus you cannot bank, and never as a reason to relax chlorine. What keeps algae out of a pool is free chlorine held at the right percentage of your CYA, every day, and borates do not change that arithmetic.

We are leaving the correction visible rather than quietly deleting the claim, because it is the more useful thing to read: something that sounds plausible, is repeated everywhere, and does not survive its own source’s current numbers.

The chlorine number does not change. Hold your floor.

There is a widely repeated claim — we repeated it here — that carrying 50 ppm of borates lets the minimum free chlorine ease from roughly 7.5% of your CYA toward about 5%, on the strength of borates adding that secondary check on algae.

We are retiring it, because it rests on the algae claim above, and the source has walked that back. TFP’s current borates guidance makes no mention of a reduced chlorine minimum at all, and their wiki’s expert contributor is direct about it: “the suggestion to maintain lower chlorine levels when using borate is risky and problematic.”

So the number to run is the number you would run without borates. Hold the 7.5% minimum of your CYA, borates or not. It is the floor you can hit every time without thinking about it, and nothing on this page buys you permission to go under it.

What borates absolutely do not do

Be clear-eyed about this part, because it is where people get hurt.

That distinction has a memorable real-world illustration. A North Texas pool professional, Deep End Frank, has described his own pool going roughly six weeks one summer without chemical service because of a scheduling mistake. When he got to it, the water was strikingly clear with no visible algae — and it tested at zero free chlorine, with a smell to match. His own conclusion is the right one and he states it plainly: do not ever run a pool that way.

What the episode does illustrate is the algaestatic effect doing its job at the margins, on a pool that had everything else going for it — strong circulation, real filtration and turnover, debris removed, brushed regularly. Borates plus good fundamentals kept an algae population from exploding into a visible bloom. Borates alone would not have.

And they do not fix any of this: poor circulation, an undersized or dirty filter, too few pump hours, no brushing, a deck full of debris blowing in, or chemistry that gets looked at once a month. Borates make a well-maintained pool easier. They make a badly-maintained pool no better.

What pros report after running them for years

The strongest case for borates is not a lab study — it is operators who run them across a lot of pools and keep doing it. Deep End Frank, whose service operation runs borates across its North Texas accounts, reports the following. We are labelling these as operator observations from one (large) service business, not as measured results: they are consistent with the known chemistry, but nobody has published a controlled study putting numbers on them.

• Materially lower overall chemical use across the operation — he puts it at roughly 25–35%, which we would read as “a large reduction” rather than as a precise figure you should expect to reproduce
• Lower chlorine demand and reduced acid demand, with pH easier to hold
• Fewer trichlor tablets needed on many pools, which matters more than it sounds: tablets quietly push CYA up until your normal chlorine stops working
• Less algae pressure, and faster recovery after storms and equipment failures
• Water that customers describe as softer and clearer

That last point about equipment failure got its biggest test during the February 2021 Texas freeze, when pumps, filters, heaters and plumbing were damaged across the Dallas–Fort Worth area and supply shortages left some pools without normal equipment operation for weeks. Borates, chlorine, robotic cleaners and whatever circulation and filtration could be kept running were enough to hold those pools through conditions that would otherwise have produced widespread algae. That is a genuinely useful signal about resilience — how a pool behaves when something breaks — which is exactly the scenario a buffer and an algaestat should help with.

Before you dose: fix the alkalinity first

Trouble Free Pool’s decision rule is worth borrowing whole, because it saves some readers the whole exercise. If your goal is less pH rise, start with TA, not borates. Bring total alkalinity toward the low end of its range — 60–80 ppm — and see how pH behaves. On a lot of pools that is enough on its own, and TA is free to lower with acid you are already buying.

TFP also says plainly what we had not: borates are not for a first-season pool. “We do not recommend borates to new pool owners; manage your pool for at least one season before considering borates.” Borates are a refinement on a pool that is already predictable, not a way to make an unpredictable one behave.

How to add borates — and which route is actually cheaper

Two routes. The received wisdom, which this page used to repeat, is that borax is the cheap one and boric acid the expensive convenience. We priced both properly in August 2026, and on a normal-size pool it comes out the other way round.

Boric acid. Granular boric acid dissolves straight to borate and moves pH slightly down, so nothing goes in beside it. Distribute across the surface with the pump running, circulate an hour, check pH. 23.9 lb takes 10,000 gallons to 50 ppm. One afternoon, one product.

Borax plus muriatic acid. Borax is a base — the acid is what converts it to borate in the water, so the acid is part of the dose, not a footnote. 10,000 gallons to 50 ppm takes 36.8 lb of borax — nine of the 65 oz laundry boxes — plus 2.3 gallons of 31.45% muriatic acid, added in stages with the pump running over a day or two: pre-dissolved borax in, acid separately and slowly over the deep end, test, repeat, then re-check pH 24 hours later.

Now the money, at Walmart and Amazon prices read the same day:

The pail is the catch: you buy all 55 lb whether you need it or not, so on a small pool the cash out the door is $131 against $100. But the borax route costs about $8.63 per 1,000 gallons while the pail is a flat $131, so above roughly 15,000 gallons one pail is cheaper outright — and it is less work at every size. On a 20,000-gallon pool it is not close: about $172 of borax and acid against one $131 pail.

Under 15,000 gallons the pail still wins on everything except the first receipt, because borates do not degrade. The 31 lb left in the bucket is next season’s top-up, not waste.

Two things worth knowing from that owner base, because we read it rather than counting it. One reviewer with a salt pool describes exactly the mechanism above, unprompted — buildup on the cell elements, boric acid buffering the pH spike inside the cell, and the “little white snowflakes” in the water being scale the cell has shed. And another publishes the dose from the field: “between 14 lbs (30ppm) and 24 lbs (50ppm) per 10,000 gallons… 55 lbs gives you approx 46 ppm which is just about perfect for a 25,000 gallon pool.” Our own figures, derived independently from molar mass, are 14.3, 23.9 and 46.1. That is a nice thing to find after you have done the arithmetic.

And the complaint tail is worth stating because of how empty it is. Filtered to critical, this listing has three reviews out of 278 — two from people who bought it to kill roaches and cave crickets and found the insects walked straight through it (plain boric acid is not a contact killer; it needs a sugar bait), and one saying it works but costs too much. Not one critical review is about pool use, purity, caking, short weight or failing to raise borates.

Her other point is the practical one: 55 lb in a pail is awkward and dusty. Scoop it out with a small bucket rather than trying to pour, and wear gloves and a mask while you do — “you don’t want to breathe in this stuff.”

If you would rather do it the grocery way, here is that route in full — but read the acid line before you decide it is the cheap one.

And skip the pool-aisle borate product. ProTeam Supreme Plus, the branded one, is sodium tetraborate pentahydrate — not the decahydrate the laundry box is — and TFP flags that it significantly raises total alkalinity while it adds borates — the opposite of what you want, given that low-end TA is the actual first move against pH rise. Boric acid barely touches TA.

Either way, run your own numbers rather than estimating. Borates are not consumed, which is their best feature and also why overshooting is a problem: the only way back down is diluting, and diluting means draining water.

How much does your pool need?

Set I want to → Raise borates, pick your route, and enter your gallons. The borax route reports the muriatic acid alongside the weight, because that is the number that decides which route is cheaper.

Testing takes a borate-specific strip. Your drop kit does not measure borates and neither does the pool store’s panel. Test after dosing, then occasionally — the level should be stable, so a drop you cannot explain is a signal in itself.

Borate strips are a genuinely thin category — there are about three of them and the best-known, Taylor’s, has two owner ratings. The one worth buying is the cheapest and by far the most-owned, and it reads a discrete 50 ppm, which is the number this whole page is written around.

But if the arithmetic checks out, the strip becomes the suspect — and we would rather say that than defend our own pick. We read this listing’s critical reviews signed-in in August 2026, and the two owners who checked it against a better instrument both found it reading low: a commercial testing lab put one pool over 30 ppm where the strip said 10, and another owner read 30 ppm on a Hach. A third dosed six boxes into 10,000 gallons — 24.4 lb, which the arithmetic above puts at 33 ppm — and still read 10. Owners also say the “ok” and “high” colour blocks are hard to tell apart, which is the same failure in gentler form.

So treat it as a band, not a number, and treat a stubbornly low reading as ambiguous rather than conclusive: it may be a half-dose, and it may be the strip. If the distinction matters to you — you are chasing the last 15 ppm, or you have dosed twice on its say-so — that is the point to spend on a LaMotte strip or a Hach kit, which is what those owners moved to. This is still the strip we would buy first, because at about a third the cost per test and 17× the owner base it is the only one in a thin category with any real evidence behind it. It is just not a precision instrument, and nothing in this category is.

Before you spend a dollar: two gates

The honest bottom line

Borates are one of the few pool additives we will straightforwardly recommend, with the caveats above intact. They buffer pH so it stops climbing, they add a real if modest check on algae, and they stay put instead of needing constant replenishment — which is the opposite of most of what the pool store sells you. They will not sanitize your pool, they will not clear a bloom, and they will not save a pool whose filter, pump schedule or brushing is the actual problem.

Get the boring things right, then add borates, and the pool gets easier to keep rather than easier to ignore. That is the whole claim, and it is a good one.

Once they’re in, log your tests in the free, on-device Pool Tracker — it judges every reading against your pool’s target and shows the trend, which is the fastest way to see the acid demand actually flatten out.