Raising total alkalinity (TA) from 60 to 90 ppm in a 15,000 gallon pool takes 6.3 pounds of baking soda, about 12 cups. Lowering it from 130 to 90 ppm takes 154 fl oz of 31.45% muriatic acid (1.2 gallons) or 12.8 lb of dry acid, added in four parts. Choose Raise or Lower above, set the target that matches your chlorine, and the amount follows.
How the alkalinity dose is calculated
Total alkalinity is measured in ppm as calcium carbonate. Each product has a fixed effect per pound or per fluid ounce, worked from its chemistry.
Product = ppm change × gallons ÷ 10,000 × product per 10 ppm per 10,000 gal ÷ 10
Baking soda (sodium bicarbonate) raises TA 10 ppm in 10,000 gallons at 1.40 lb by stoichiometry. The NSPF table in the Indiana State Department of Health guide gives 1.4 lb, PHTA and label sheets round it to 1.5 lb. For 30 ppm in 15,000 gallons: 3 × 1.5 × 1.40 lb = 6.30 lb. In cups that is about 12, because baking soda packs at about 1 g per mL and cup figures for solids are approximate.
Muriatic acid at 31.45% lowers TA 10 ppm at 25.6 fl oz per 10,000 gallons (PHTA quotes 1.6 pints, which is 25.6 fl oz). For 40 ppm in 15,000 gallons: 4 × 1.5 × 25.6 = 153.8 fl oz. Dry acid (sodium bisulfate 94%) is 2.1 lb per 10 ppm: 12.8 lb for the example.
The TA target: where authorities differ
| Source | Target |
|---|---|
| PHTA (followed here) | 80 to 100 ppm with hypochlorite, cal-hypo or salt chlorine; 100 to 120 ppm with dichlor, trichlor or bromine; acceptable 60 to 180 ppm |
| Hayward, Pentair, CircuPool manuals | 80 to 120 ppm |
| Trouble Free Pool | about 50 to 90 ppm, because cyanuric acid already counts in TA |
PHTA gives a reason for the two bands: dichlor, trichlor and bromine push pH down, so they need more buffer, while hypochlorite and salt chlorine push it up. The low-TA camp is explained by cyanurate: in a stabilized pool part of your TA reading is cyanuric acid, which is not the carbonate alkalinity that scale and etching depend on. PHTA gives the correction, carbonate alkalinity = TA minus a CYA share that depends on pH, and about one third of CYA as a shortcut. Enter pH and CYA in the calculator and it shows your carbonate alkalinity.
Order matters: TA first, then pH
PHTA says total alkalinity should be corrected before you adjust pH or sanitizer. TA is the buffer for pH: with low TA the pH swings, with high TA it climbs. That is why the pool pH calculator asks for your TA.
Raising TA in parts
The Indiana guide says not to raise TA more than about 50 ppm at once. If your rise is bigger, the calculator splits it into equal additions. Spread baking soda across the deep end with the pump running, let it circulate, retest, and add the next part. Baking soda raises pH only slightly. Soda ash is different: it raises pH strongly and TA as well, which is why the pH tool uses it.
Lowering TA: acid and aeration
Acid lowers TA and pH together. Enter your pH and the tool shows about where it lands: with TA 130, pH 7.6 and CYA 30, removing 40 ppm of TA takes pH far below range in the model. That is not a mistake: the usual method is to add acid in small parts, then aerate. Aeration lets carbon dioxide leave the water, which raises pH without changing TA. Swim University describes it as pointing the returns upward or running a fountain. Repeat until TA and pH are both where you want them.
The Indiana guide limits one addition of liquid acid to 1 quart per 10,000 gallons and says to retest about 12 hours later. Swim University allows half a gallon per session; we follow the smaller limit. Handling notes are in the muriatic acid pool calculator, which also shows 14.5% acid.
Metric
In litres, the 40 ppm drop in 56.8 m³ is 4.5 L of 31.45% acid, and the 30 ppm rise is 2.9 kg of baking soda.
What to do next
Once TA is set, use the LSI calculator to check the water is neither scaling nor etching, and the pool calcium hardness calculator if hardness is off. Put all your readings in the pool chemical calculator, and start with your gallons from the pool volume calculator. See the pool chemistry hub for the rest.