What does borax do in a pool?
Borax raises pH and, at a high enough level, buffers the water so pH stays put. It is an alkaline salt, so the moment it dissolves it pushes pH up. The common source is 20 Mule Team Borax, the laundry booster, which is essentially pure sodium tetraborate with nothing else added, which is why pool owners use it instead of a branded pool product that costs several times more for the same chemical.
Its second job shows up only once there is enough of it in the water. At a borate level of 30 to 50 ppm, borates act as a secondary pH buffer, resisting the upward pH creep that plagues saltwater pools and any pool running trichlor or plenty of aeration. That same borate reserve is a mild algaestat: it slows algae growth, so it supplements your chlorine rather than replacing it. Many owners also report the water feels softer and looks brighter at that level.
What borax will not do is sanitize the pool. It kills nothing and does not oxidize contaminants, so chlorine is still the thing keeping the water safe to swim in. Think of borax as a chemistry stabilizer that makes your sanitizer's life easier, not as a sanitizer itself. If your free chlorine is low, size the fix with the pool chlorine calculator; borax does not change that job.
Borax vs soda ash: which should you use to raise pH?
Use borax when your pH is low but your total alkalinity is already fine or high, and soda ash when both need to come up. Both raise pH, but soda ash (sodium carbonate) raises total alkalinity right alongside it, while borax nudges pH up with a much smaller alkalinity bump. So if your alkalinity is sitting comfortably in range and you only need to lift pH, soda ash would overshoot your alkalinity and borax will not.
This is the same logic that separates soda ash from baking soda, laid out in soda ash vs baking soda: match the chemical to which number is actually off. Before you add anything, confirm what needs to move. Check where your alkalinity stands with the alkalinity calculator and size the pH change with the pool pH calculator, then pick borax if pH is the only number that is low.
One caution: borax works slowly compared to soda ash. It takes longer to dissolve and register on a test, so give it time and circulation before you decide it did not do enough. Chasing it with more product before the first dose has fully mixed is how people overshoot pH and then have to bring it back down with acid.
How much borax do you add, and how do you add it?
The amount depends on how far your pH needs to move and whether you are just correcting pH or building a full borate reserve to 30 to 50 ppm. A small pH correction takes very little; reaching the borate target takes far more, several pounds in an average backyard pool. Rather than guess at a number, size the pH change with the pool pH calculator, add the borax in stages, and retest before adding more. If you are aiming for a borate level, check it with borate test strips instead of eyeballing it.
Add it the same careful way you add any pool chemical. Pre-dissolve the borax in a bucket of warm water, or broadcast it slowly across the deep end with the pump running, and brush any that settles on the floor so it does not sit in a pile. Borax dissolves slowly, especially in cool water, so a pile left on a vinyl or plaster floor can bleach a mark before it dissolves. Keep the water moving and give it several hours.
Then retest and adjust. Never dump a full calculated dose at once and call it done. Add part of it, run the pump to mix, wait, and test again, because pH that reads low in a cool morning sample can climb on its own as the water warms and aerates. Adding in stages is the whole safeguard against overshooting and then fighting your own correction with muriatic acid.
What is the borate method, and is it worth it?
The borate method is dosing your pool to a borate level of 30 to 50 ppm to gain a pH buffer and a mild algaestat. It is worth it if you are tired of your pH climbing every few days, if you run a saltwater or high-aeration pool, or if you fight recurring algae. The payoff is steadier pH (less soda ash and acid chasing), a mild brake on algae that lets your chlorine work less hard, and water that many people find softer and clearer.
There are two ways to get there. Borax plus muriatic acid is the cheap route: the borax raises the borate level but also spikes pH, so you add acid to bring pH back down, and you repeat until the borate strip reads in range. The acid side of that is covered in how to lower pH in a pool, and muriatic acid vs dry acid covers which acid to use. Boric acid is the tidier route: it adds borate with almost no pH change, so you skip most of the acid, but it costs more and is harder to find locally.
The trade-offs are real. Borates cost money up front, need their own test strips, and do nothing for sanitation, so they are an upgrade, not a fix for a neglected pool. A pool with an algae problem needs the algae cleared with chlorine first; borates prevent, they do not cure. If your pH is stable and your pool is easy to keep, you may never need them.
Is borax safe to swim in, and is it safe for pets?
Borax is safe to swim in at pool levels once it has dissolved and pH has settled back into the 7.2 to 7.8 range, which usually takes a few hours with the pump running. There is no long wait like a chlorine shock; the concern is not the borate itself at 30 to 50 ppm but the temporarily high pH right after you add borax, so test and let pH come back down before anyone gets in.
The honest caveat is pets. Borates are toxic to dogs if they drink a real quantity of pool water, and a dog that treats the pool as a water bowl can take in enough to make it sick over time. Keep the borate level at the 30 to 50 ppm target rather than higher, and discourage pets from drinking the pool. For swimmers, including children, borates at pool levels are considered safe; the water is not something anyone should be gulping regardless.
One more practical note: borates can throw off a few test methods and a saltwater cell's calibration slightly, so use borate-specific strips to read the level and keep an eye on your other numbers after you first dose. None of that is dangerous, but it is worth knowing so a surprise reading does not send you chasing a problem that is not there.
Boric acid vs borax: what is the difference?
They end up as the same borate in your water, but borax is alkaline and raises pH, while boric acid is acidic and slightly lowers it. That single difference decides how you use each one. Borax spikes pH as it dissolves, so the borax route to a borate level means adding acid afterward to bring pH back. Boric acid reaches the same borate level with almost no pH swing, so you skip most of the acid dance.
So which is better depends on convenience and price. Borax (the 20 Mule Team box) is cheap and on the shelf at any grocery store, which is why most DIY borate dosing starts there. Boric acid costs more and usually has to be ordered, but it saves you the acid and the pH juggling, so it is the cleaner choice if you can get it. For simply raising pH a little, plain borax is the obvious pick; for building a full borate reserve without a pH rollercoaster, boric acid earns its price.
And to answer the common mix-up: 20 Mule Team Borax is borax, essentially pure sodium tetraborate, not boric acid and not a blend. It is the same sodium tetraborate sold in pricier pool-branded jugs, which is exactly why pool owners buy the laundry box instead. Read the label to confirm sodium tetraborate is the only ingredient, then treat it as your pH raiser or your borate source.
Frequently asked questions
Why would you put borax in a pool?
Two reasons. As a quick fix, borax raises pH when it is low but your total alkalinity is already fine, because it lifts pH with only a small alkalinity increase where soda ash would push both up. As an upgrade, dosing the water to a borate level of 30 to 50 ppm adds a pH buffer that keeps pH from drifting up so fast, acts as a mild algaestat that supplements your chlorine, and makes the water feel softer. It does not sanitize, so it never replaces chlorine.
How much borax for a 10,000 gallon pool?
It depends on how far your pH needs to move and whether you are just nudging pH or building a full borate reserve to 30 to 50 ppm. A small pH correction takes very little; the full borate method takes several pounds. Rather than guess, size the pH change with the pool pH calculator, add the borax in stages with the pump running, and retest before adding more. If you are aiming for a borate level, measure it with borate test strips instead of eyeballing the amount.
How long after putting borax in the pool can you swim?
Usually a few hours, once the borax has fully dissolved and pH has settled back into the 7.2 to 7.8 range with the pump running. Unlike a chlorine shock there is no long lockout; the only thing to wait on is the temporary pH spike right after you add borax. Test the water, and once pH is back in range and the borax is dissolved with nothing piled on the floor, it is fine to swim.
Which is better for swimming pools, borax or soda ash?
Neither is better overall; they do different jobs. Use borax when your pH is low but total alkalinity is already in range, because it raises pH with a smaller alkalinity bump. Use soda ash when pH and alkalinity are both low, since it raises the two together and works faster. Borax is also the chemical you use for the borate method, which soda ash cannot do. Check both numbers with the alkalinity and pH calculators, then pick the one that matches what is actually off.
What should you never mix with borax?
Never mix borax directly with any other pool chemical in a bucket or feeder, especially not acid or chlorine. The borate method deliberately uses borax and muriatic acid together, but you add each one separately to the pool water with the pump running and wait between them; you never combine concentrated chemicals, which can react violently or release fumes. Add borax to water, circulate, then add anything else on its own.