Find out how much borax or boric acid to add to reach your target borate level, and how much muriatic acid to bring pH back down afterward. If your borates are already too high, it shows how much water to replace instead.
Enter your pool volume and current borate reading (use 0 if you have never added borates).
Not sure of your pool volume? Use our pool volume calculator. Need to check pH after dosing? Try the pool pH calculator.
- Test borates, pH and total alkalinity first, and correct alkalinity before you start.
- Pre-dissolve the borax (or boric acid) in a bucket of warm water. It dissolves slowly in cold pool water.
- With the pump running, pour the solution slowly around the deep end, in front of the return jets. Never put it in the skimmer.
- If you used borax, add the muriatic acid in small portions in a different spot, and retest pH between portions.
- Run the pump for 24 hours, then retest borates. Add a second, smaller round only if you are still under target.
Pool Borax Dosage Chart: Pounds by Pool Size and Target Level
Amounts assume a pool starting at 0 ppm borates and are in pounds (lbs), using 7.375 lb of borax or 4.75 lb of boric acid per 10 ppm in 10,000 gallons. Already have some borates? Enter your reading in the calculator above.
Borax and muriatic acid
| Pool Volume | To 30 ppm | To 40 ppm | To 50 ppm | Acid for 50 ppm (fl oz) |
|---|---|---|---|---|
| 5,000 gal | 11.1 | 14.8 | 18.4 | 148 |
| 7,500 gal | 16.6 | 22.1 | 27.7 | 221 |
| 10,000 gal | 22.1 | 29.5 | 36.9 | 295 |
| 15,000 gal | 33.2 | 44.2 | 55.3 | 442 |
| 20,000 gal | 44.2 | 59.0 | 73.8 | 590 |
| 25,000 gal | 55.3 | 73.8 | 92.2 | 738 |
| 30,000 gal | 66.4 | 88.5 | 110.6 | 885 |
| 40,000 gal | 88.5 | 118.0 | 147.5 | 1,180 |
Acid is 31.45% muriatic acid, about 0.5 fl oz per oz of borax, enough to turn all of the borax into boric acid. Add it in portions and retest pH, since your starting pH also matters.
Boric acid
| Pool Volume | To 30 ppm | To 40 ppm | To 50 ppm |
|---|---|---|---|
| 5,000 gal | 7.1 | 9.5 | 11.9 |
| 7,500 gal | 10.7 | 14.2 | 17.8 |
| 10,000 gal | 14.2 | 19.0 | 23.8 |
| 15,000 gal | 21.4 | 28.5 | 35.6 |
| 20,000 gal | 28.5 | 38.0 | 47.5 |
| 25,000 gal | 35.6 | 47.5 | 59.4 |
| 30,000 gal | 42.8 | 57.0 | 71.2 |
| 40,000 gal | 57.0 | 76.0 | 95.0 |
Boric acid needs less weight than borax and barely moves pH, so no muriatic acid is needed.
Borates too high? Water to replace
| Current Level | Down to 50 ppm | Down to 40 ppm | Down to 30 ppm |
|---|---|---|---|
| 60 ppm | 17% | 33% | 50% |
| 70 ppm | 29% | 43% | 57% |
| 80 ppm | 38% | 50% | 62% |
| 100 ppm | 50% | 60% | 70% |
| 120 ppm | 58% | 67% | 75% |
Percent of the pool’s water to drain and replace with fresh water. Borates do not evaporate, so this is the only way to bring the level down.
Pool Borates FAQs
Borax does two different jobs depending on how much you use. In a small dose it raises pH, because borax is alkaline (about pH 9.2) while barely moving total alkalinity. Built up to 30 to 50 ppm borates, it steadies pH against drift, helps discourage algae growth and gives the water a softer, clearer look. It is not a sanitizer, so you still need chlorine.
Yes. Borax is alkaline, so it raises pH every time you add it, which is why a borate program using borax ends with muriatic acid to bring pH back down. If you want borates without the pH rise, use boric acid instead. Retest after the pump has run for several hours, because the full pH change takes a while to show.
A little, but far less than it raises pH. Baking soda is the product for raising total alkalinity, and borax is the better pick when pH is low but alkalinity is already in range. Test both pH and alkalinity again after 24 hours of circulation rather than assuming.
The powder dissolves slowly, faster in warm water, and anything that settles on the floor can leave a cloudy patch until it is brushed around. pH climbs within hours and the borates stay in the water afterward. They do not evaporate or get used up, so the level only falls through splash-out, backwashing and refilling. Overshoot 50 ppm and the only fix is replacing water.
Once the borax has fully dissolved and circulated, usually 30 to 60 minutes with the pump on high, and your pH reads in the normal range. If you also added muriatic acid, let that circulate too and retest first. Boric acid follows the same rule.
You can use both in the same pool, and mixing the two powders is not dangerous, but add them separately instead of premixed because they fix different problems. Baking soda raises alkalinity and borax raises pH. Correct alkalinity first, let the water circulate and retest, then add borax only if pH is still low.
Both leave the same borates behind. Borax is cheaper and easy to find, but it raises pH so you need muriatic acid alongside it. Boric acid costs more per pound but takes less weight (about 4.75 lb versus 7.4 lb per 10 ppm in 10,000 gallons) and barely changes pH. Choose boric acid if your pH is already at the top of the range.
Not on its own. Borates slow algae growth and make chlorine’s job easier, but they will not clear an existing bloom. Treat the bloom with chlorine shock and brushing first, then build borates to 30 to 50 ppm to help prevent a repeat.
At the usual 30 to 50 ppm, borates are considered fine for swimming, but the water is not something to drink. Stay at or under 50 ppm, keep dry borax and boric acid away from children and pets, and discourage pets from drinking pool water. If the level overshoots, replace water using the figure from the calculator.
