Borates
Also called: borate, boric acid, borax.
Borates are a pH buffer added to pool water as boric acid or borax and held at 30–50 ppm. Borates slow the upward pH drift every pool has and cut scale inside a salt cell. Borates do not sanitize, and they do not let a pool run less chlorine.
Why it matters
Trouble Free Pool is clear that borates take the same amount of acid over a season; what drops is how often you dose. Nothing uses them up, so the level only falls when water leaves the pool, and overshooting is only undone by draining. The algae claim is overstated at pool levels, so hold free chlorine at 7.5% of your CYA, borates or not. Bring total alkalinity to the low end of its range first; on many pools that is the whole fix. Test with a borate-specific strip. Buy granular boric acid, never powdered, and never an insecticide product.
In numbers
Granular boric acid: 23.9 lb per 10,000 gallons reaches 50 ppm, with no acid alongside. The borax route takes 36.8 lb of borax plus 2.3 gallons of 31.45% muriatic acid for the same 10,000 gallons.