How the calculation works
Borate is measured as boron, and boric acid is 17.48% boron by weight. Raising 10,000 gallons by 10 ppm therefore takes about 4.8 lbs of boric acid — scaled up for a bigger pool and down for a purer product.
Worked example
A 20,000 gallon pool starting at zero, aiming for 40 ppm. That is 4.8 × 4 × 2 = roughly 38 lbs of boric acid. It is a large one-off dose; borates are not consumed, so the level only falls as water is lost.
Assumptions
- Doses are calculated from the product strength you selected, not a generic chart.
- Pool volume is accurate — a volume that is out by a quarter puts every dose out by a quarter.
- Water is circulating while the chemical is added and for several hours afterwards.
- Borate is measured as boron, which is how most pool test kits report it.
- Boric acid is the product used. Borax plus acid reaches the same place by a different route and takes different arithmetic.
Limitations
- Test kits vary. Strips are convenient but a drop-based kit is markedly more reliable for anything beyond a rough check.
- Products degrade. Liquid chlorine loses strength within weeks of manufacture, especially in heat, so an older jug delivers less than its label claims.
- These figures are estimates for a typical residential pool, not a prescription for your specific water.
- Borates are optional. A pool with alkalinity and pH in range does not need them — they make pH easier to hold, they do not fix anything that is broken.
- Like salt and cyanuric acid, borate is never consumed. Only water loss brings it down.
Questions people ask
What do borates do?
They act as a second buffer alongside alkalinity, holding pH steady around 7.5 instead of letting it creep upward. Pools with salt chlorinators or water features — both of which drive pH up — benefit most.
Are borates safe to swim in?
At 30 – 50 ppm they are widely used in residential pools and considered safe for swimmers. The genuine concern is dogs, which may drink enough pool water for it to matter.
Do I need borates?
No. They are a convenience, not a requirement. If your pH sits still on its own, there is nothing for them to improve.
How do I test borate?
With borate test strips — most standard kits do not include the test. Check the level before dosing, since borates accumulate and cannot be removed.