Alkalinity Calculator
Calculate how much baking soda or muriatic acid to add to adjust your total alkalinity to the ideal 80-120 ppm range.
Safety
Add baking soda in doses of no more than 2.5 lbs at a time. Wait 6–8 hours between doses and retest. For acid, add with pump running, distribute evenly, and never mix with other chemicals.
To raise total alkalinity, add about 1.5 lb of baking soda per 10,000 gallons for every 10 ppm you need. Baking soda (sodium bicarbonate) lifts TA with almost no effect on pH — to raise pH itself, use soda ash. Enter your pool's numbers above for the exact amount.
Fix Alkalinity Before You Chase pH
Total alkalinity is the water's resistance to pH change. It is not a target you hit for its own sake — it is the reason pH either stays where you put it or drifts back within a day. Anyone adding acid every few days and watching pH climb again is not fighting a pH problem. They are fighting a TA problem with the wrong chemical.
Aim for 80–120 ppm. Plaster and pebble pools are usually happier at the top of that band or slightly above; vinyl and fiberglass sit comfortably at the bottom. Salt pools generally do better nearer 70–80, because the cell pushes pH up on its own and a low buffer means less acid to hold it down.
What each end of the range actually does
Too low and there is nothing holding pH in place: a rainstorm, a heavy swim day or a dose of acid sends it lurching, and water below roughly 60 ppm turns aggressive — it pulls calcium out of plaster and grout to buffer itself, which shows as etching and rough patches. Too high and the buffer works against you: pH creeps upward and refuses to stay down, scale forms on the tile line and the salt cell, and chlorine works more slowly at the pH the water settles at.
Raising it: baking soda, and nothing exotic
1.5 lb of sodium bicarbonate per 10,000 gallons raises TA about 10 ppm. Pool-store "alkalinity increaser" and the yellow box of Arm & Hammer are the same compound at very different prices — check that the label says sodium bicarbonate and buy whichever is cheaper per pound. It moves pH barely at all, which is exactly why it is the right tool: you can correct the buffer without disturbing the number sitting on top of it.
Broadcast it slowly over the deep end with the pump running, and cap each addition at about 2.5 lb. Bigger single doses cloud the water and settle before they dissolve. Wait 6 to 8 hours between doses and retest — TA readings lag the addition, and dosing again on a stale reading is how a pool at 60 ends up at 160.
Alkalinity Dose Chart
How much of each chemical moves TA by a given amount, at two common pool sizes.
| TA change | Baking soda 10k gal |
Baking soda 20k gal |
Muriatic acid 10k gal |
Muriatic acid 20k gal |
|---|---|---|---|---|
| 10 ppm | 1.5 lb | 3.0 lb | 25 fl oz | 50 fl oz |
| 20 ppm | 3.0 lb | 6.0 lb | 50 fl oz | 100 fl oz |
| 30 ppm | 4.5 lb | 9.0 lb | 75 fl oz | 150 fl oz |
| 40 ppm | 6.0 lb | 12.0 lb | 100 fl oz | 200 fl oz |
| 50 ppm | 7.5 lb | 15.0 lb | 125 fl oz | 250 fl oz |
| 60 ppm | 9.0 lb | 18.0 lb | 150 fl oz | 300 fl oz |
Muriatic acid at 31.45%. Acid lowers pH along with TA, so the acid columns are a starting point for a cycle rather than a single dose — see below. Enter your own volume above for the exact figure.
Lowering it: acid, then air
There is no chemical that removes alkalinity and leaves pH alone. Acid takes both down together, which is why lowering TA is a cycle rather than a dose: add acid, let pH fall to around 7.0–7.2, then aerate — run a spa jet, a fountain, a return aimed up at the surface, or simply brush and agitate the water. Aeration drives off dissolved carbon dioxide, and pH rises back toward 7.4 while TA stays where the acid left it. Repeat until TA lands in range.
It takes days rather than an afternoon, and the pool is perfectly usable throughout. Add acid with the pump running and pour it slowly across the deep end, never into a skimmer, and never alongside chlorine.
When it keeps coming back
TA that climbs after every correction usually has a source. Test the fill water — a lot of municipal supplies run 120 ppm or higher, so every top-up and every backwash refills the buffer you just removed. New plaster leaches for its first season. Trichlor tabs and acid pull TA down over time, while cal-hypo and soda ash nudge it up, so the products in your routine set the direction the water drifts.
Once TA sits in range, pH becomes a much smaller job — work it out with the pH calculator, or run the whole panel in the correct order with the water balance calculator. If you are reaching for baking soda often, the baking soda guide covers what it can and cannot fix. Unsure whether your problem is alkalinity or pH? Baking soda vs soda ash lays out which chemical fixes which.