Borates are the quiet upgrade a lot of pros add once the basics are dialed in: a second pH buffer that fights the slow drift upward, a mild algae suppressant, and that "sparkle" and softer feel to the water. Here's the level to aim for, boric acid versus borax, how much to add, and how to do it safely.
What borates do
Borates work on three fronts. They act as a secondary pH buffer — on top of your alkalinity — that resists the steady climb in pH, which is a real help on pools with a chlorine generator or lots of aeration, where pH constantly wants to rise. They're a mild algaestat, making it harder for algae to get a foothold. And many owners notice the water looks brighter and feels softer. Borates don't sanitize, though — they're an add-on to chlorine, not a replacement.
The ideal range
Aim for 30–50 ppm borate. Below about 30 ppm you get little of the buffering or algae benefit; above 50 ppm there's no added value, so there's no reason to push past it. Test with borate test strips — a standard test kit won't read borate.
Boric acid vs. borax
Two ways to get there:
- Boric acid (easiest). It's essentially pH-neutral, so you just add it and retest — no pH juggling. This is what our calculator doses.
- Borax + muriatic acid (cheaper). Borax (sodium tetraborate) is inexpensive but drives pH sharply up, so you have to add muriatic acid to bring pH back down. It works, but it's a two-chemical balancing act — follow acid-handling safety carefully.
How much to add
The math our calculator uses: about 1.7 lb of boric acid per 10,000 gallons raises borate roughly 10 ppm. So taking a 20,000-gallon pool from 0 to 50 ppm is about 17 lb of boric acid. Enter your own numbers for the exact amount. Borate calculator →
Step by step
- Balance first. Get chlorine, pH, and alkalinity in range before you add borates.
- Run the pump the whole time so the water is circulating.
- Broadcast it over the deep end and brush any that settles — boric acid dissolves slowly.
- If you're using borax, add the muriatic acid separately to offset the pH rise: acid into the water (never water into acid), pump running, and never near chlorine.
- Let it circulate, then retest with borate strips after a full turnover before adding any more.
Safety & don't overshoot
At swim-level concentrations the water is fine for people, but borate is toxic to dogs and to plants — keep pets from drinking pool water and don't drain borate water onto the garden. And like CYA, borate only comes down by dilution, so add a little less than you think, retest, and top up. Always confirm doses and handling against your product label.