Pool Alkalinity Calculator

Baking soda to raise it, acid + aeration to lower it without wrecking pH. The same engine the pH calculator uses — one engine, two doors.

Hook

Alkalinity is the most ignored number in pool care — right up until your pH starts swinging wild on every rainstorm, every shock, every splash.

Total alkalinity is the shock absorber that keeps pH still. Get it right and pH stops fighting you. Get it wrong and you'll chase pH all summer.

Promise

This calculator gives you the exact dose — baking soda to raise alkalinity, acid to lower it — with the one thing the dosing charts skip: what it does to your pH. You'll see why baking soda is the right tool for alkalinity (and soda ash isn't), how to lower alkalinity without wrecking your pH, and where the number actually needs to sit. Real chemistry, every figure derived on the page.

Here's the deal: raising alkalinity is easy and precise — baking soda, weighed to your water. Lowering it is the tricky half, because the only thing that lowers alkalinity is acid — and acid drops pH too. The fix isn't a secret chemical; it's a sequence. We'll show you both.

What you'll give us

Three numbers: your gallons, your current TA, and your target TA. Optional fourth: your current pH, which sharpens the reagent recommendation. The diagram below shows the RAISE flow; the calculator swaps it for LOWER when target < current.

RAISE is the precise half: baking soda, weighed to your pool size, broadcast across the surface with the pump running. The branded “alkalinity increaser” you might be price-comparing is the same chemical.

The calculator

Pick a mode, fill the fields, hit calculate. The acid-safety banner pins above the acid selector when you're lowering — identical wording to the pH page's F14, identical hazard.

Don't know your gallons? Pool volume calculator — two minutes, any shape, deep-links straight back here with ?gal= prefilled.

Why alkalinity matters — the buffer reservoir

On the pH calculator, pH was the symptom and TA was the hidden cause. Here we flip the camera: TA is the lever, pH is the thing that moves when you pull it.

Shallow reservoir, restless ball. Deep reservoir, ball stuck high and scaling everywhere. The middle one is the goal: enough depth for the ball to stop rolling, not so much it can't move when you actually need it to. That depth is total alkalinity, and 80–120 ppm is the band that holds.

TA too low

The ball rolls on every input — rain, shock, swimmer load. You'll re-test pH after every weather event and probably grab the acid jug when you should be reaching for baking soda.

TA too high

pH gets stuck near the top of the band and the carbonate system tips toward scaling. Calcium deposits show up on heater elements, salt cells, and tile lines.

Right depth (80–120)

pH sits in the 7.4–7.6 band and stays there. The same TA reading is one of the four primary inputs to the Langelier Saturation Index (LSI) — when the LSI calculator ships, this number feeds it directly.

Baking soda vs soda ash — pick the right lever

Most "alkalinity" mistakes are really reagent-selection mistakes. The two chemicals look like alternates on a store shelf — they aren't.

Same family of bases, different vectors. Baking soda pushes mostly upward — TA rises, pH barely moves. Soda ash pushes diagonally — pH up strongly, TA up too as the side effect. Match the lever to the problem: alkalinity low and pH fine, you want the blue arrow. pH low and TA also low, you want the orange one.

Reagent selection by which value is off and where pH sits
Your situation	Reach for	Why
TA low, pH okay	Baking soda	Raises TA strongly, pH barely
TA okay, pH low	Soda ash / aerate	pH up without over-raising TA
Both low	Baking soda first, then reassess	Baking soda often nudges pH up enough on its own
TA high (pH anything)	Acid + aerate	Only acid lowers TA; aerate to reclaim pH
TA inside 80–120	Nothing	Don't chase the middle

Aside · branded “alkalinity increaser”

Read the back panel. "Alkalinity up," "TA increaser," "alkalinity plus" — overwhelmingly the active ingredient is sodium bicarbonate, the same chemical as the baking soda in your kitchen aisle. The dose math is identical; the price is rarely identical. We can't name brands without naming a specific brand — but the general truth holds across the category.

Lower alkalinity without crashing pH — acid down, air up

The query the dosing charts shrug at, finally answered correctly. The fix is a sequence, not a special chemical.

The two steps that decouple TA from pH. Acid drops both — that's unavoidable, they're the same physical neutralization. Aeration only walks pH back, because CO₂ off-gassing changes the carbonate ratio without removing any alkalinity. Same trick the pH page's bounce-back explainer describes from the other side.

The trap: the only thing that lowers alkalinity is acid, and acid lowers pH at the same time. So "lower my TA but keep my pH" sounds impossible — and the clones just shrug. It isn't impossible; it's a two-step sequence.

Step one: dose acid to your TA target. Your pH will dip — let it. The dose comes from the same coefficient the pool pH calculator uses; it's the same physical neutralization seen from the TA side.

Step two: aerate. Point your returns up, run a fountain or jets at the surface. The agitation off-gasses CO₂, which walks pH back up while your alkalinity stays right where you dropped it.

The payoff line

Acid down, air up.

You target TA with the acid; you reclaim pH with aeration, for free. The pH calculator covers the rebound mechanism from the pH side — same physics, complementary view.

Where the baking-soda number comes from

The same show-the-math move the volume and pH pages do. Five steps, one stoichiometric truth, ending in the sanity check that everyone's pool-store chart already knows.

Step 1 · alkalinity basis
Total alkalinity is reported as ppm CaCO₃. By the APHA Standard Methods titration: 1 meq/L of acid-neutralizing capacity = 50.04 ppm as CaCO₃. Same constant the pool pH calculator uses — one engine.
Step 2 · raise direction
To raise TA by ΔTA ppm you add ΔTA ÷ 50.04 meq of bicarbonate per litre. Baking soda dissolves and gives one HCO₃⁻ equivalent per formula unit.
Step 3 · baking soda's formula weight
Sodium bicarbonate is NaHCO₃, MW 84.007 g/mol (CRC). Retail product is ~pure — no purity divisor needed at the homeowner scale.
Step 4 · volume
Litres from gallons (NIST exact): V_L = V_gal × 3.78541.
Step 5 · put it together
lb of NaHCO₃ = (ΔTA ÷ 50.04) × (V_gal × 3.78541) × 84.007 ÷ 1,000 ÷ 453.592.
Step 6 · sanity check
10,000 gal, raise TA by 10 ppm → 1.401 lbof baking soda. The pool-store rule of thumb says "about 1.5 lb" for this case; we're saying 1.40. The store rule rounds up for safety; we're showing the exact stoichiometric value. Both are right for what they are.
For the LOWER path
The acid dose to lower TA is the same coefficient the pH calculator uses (mL = 0.0075648 × ΔTA × gal at 31.45% strength). Both calculators call the same muriaticDoseMl() function from lib/dosing/acidbase.ts. They cannot disagree by construction — the build pipeline asserts this, ten fixtures, every push.

Worked examples — eight common scenarios

Every number below comes from the shared engine — run any of these through the calculator above and the answer lands in the same place. The takeaway is what you'd say to a friend who showed up at your pool with a test kit.

Example 1

How much baking soda to raise alkalinity (the common case)

10,000 gal · TA 50 → 90 (ΔTA 40) · baking soda.

5.60 lb (89.7 oz · 2.54 kg)

Engine: bakingSodaTaRaiseLb(40, 10,000) = 5.60 lb. Broadcast it across the deep end with the pump running.

Don't dump in one spot — broadcast and let circulation do the mixing. Retest after a few hours.

Example 2

How much baking soda for a 20,000 gallon pool

20,000 gal · TA 60 → 100 (ΔTA 40) · baking soda.

11.21 lb (5.08 kg)

Same coefficient as E1, twice the volume → twice the dose. Engine: bakingSodaTaRaiseLb(40, 20,000) = 11.21 lb.

Over 5 lb — split into two additions a few hours apart, retest between rounds. Easier to land on target than to claw back an overshoot.

Example 3

Hot tub alkalinity calculator (tiny doses)

400 gal spa · TA 50 → 80 (ΔTA 30) · baking soda.

0.17 lb ≈ 2.7 oz

Engine: bakingSodaTaRaiseLb(30, 400) = 0.17 lb. At spa scale a careless scoop is a big overshoot.

Under three ounces. Measure, add, retest. The calculator flags spa-size volumes automatically.

Example 4

Pool alkalinity calculator in litres (metric)

50 m³ = 50,000 L (≈ 13,209 gal) · TA 40 → 90 (ΔTA 50) · baking soda.

4.20 kg (9.25 lb)

Engine: bakingSodaTaRaiseLb(50, 13,208.6) = 9.25 lb = 4.20 kg. Metric is the cleaner path — no gallon step.

~4.2 kg, broadcast in two passes. EU/AU pools land here naturally.

Example 5

How to lower alkalinity without lowering pH (the money query)

20,000 gal · TA 200 (way high) · pH 7.6 (fine). Lower TA to 120 (ΔTA 80) · 31.45% muriatic.

≈ 3.20 gal of acid — staged hard, never at once

Engine: muriaticDoseMl(80, 20,000, 10) = 12,104 mL. pH will dip during dosing (acid hits both). Then aerate — returns up, run features — to walk pH back to ~7.6 while TA stays at the new 120.

Acid down, air up. You can't lower TA without temporarily moving pH, but aeration gives the pH back for free. The pH-side framing of this same move is the headline section on the pool pH calculator.

Example 6

Dry acid to lower alkalinity (the material cost)

15,000 gal · TA 150 → 100 (ΔTA 50) · dry acid (NaHSO₄, 93%).

≈ 16.1 lb of dry acid

Engine: dryAcidDoseLb(50, 15,000) = 16.1 lb. Vs ~1.50 gal of muriatic for the same drop.

Dry acid is easier to handle but it's a lot of material for a big alkalinity drop — and every pound leaves sulfate behind permanently. For large reductions, liquid muriatic is far more practical.

Example 7

Both pH and TA low — what's the efficient first move?

12,000 gal · TA 50 (low) · pH 7.0 (low). Raise TA 50 → 90 (ΔTA 40).

6.72 lb baking soda

Engine: bakingSodaTaRaiseLb(40, 12,000) = 6.72 lb. Recheck pH after circulation — baking soda nudges pH up gently while doing most of the TA work.

When both are low, baking soda is the efficient first move. It does most of the work and frequently fixes pH as a bonus. If pH is still low after, a small soda-ash dose finishes the job — and the precise soda-ash mass for a specific pH target lives on the pH calculator.

Example 8

Does baking soda raise pH? (the differentiator, worked)

10,000 gal · TA 70 → 100 (ΔTA 30) · current pH 7.5 · baking soda.

4.20 lb baking soda

Engine: bakingSodaTaRaiseLb(30, 10,000) = 4.20 lb. Your pH stays roughly where it is — bicarbonate buffers near pool pH, so it lifts TA strongly while barely touching a normal pH. That's exactly why it's the alkalinity tool and soda ash isn't.

Baking soda = alkalinity with a tiny pH nudge; soda ash = big pH push. Match the chemical to the problem. We give direction only — no decimal predicted pH, that depends on CO₂/aeration we can't model.

Reference tables

Three crawlable tables, CC BY 4.0. Every cell renders from the shared engine — no static numbers in this file. Cite us, link back.

Two nested bands: a pale-green acceptable range (60–180) and the deeper-green typical band (80–120) inside it. The red dashed line at 65 ppm is the weak-buffer floor: below it the carbonate system stops absorbing inputs and pH starts swinging on small changes. The calculator warns rather than silently dosing a target below that line.

T1 · Baking soda to raise TA (lb)

Stoichiometric pure NaHCO₃. Real product is ~99% pure; the rounding is invisible at the homeowner scale. Stage anything over 5 lb.

Pounds of baking soda required to raise total alkalinity by ΔTA in pounds, by pool volume
Pool size (gal)	+ 10 ppm	+ 20 ppm	+ 30 ppm	+ 40 ppm
5,000	0.70	1.40	2.10	2.80
10,000	1.40	2.80	4.20	5.60
15,000	2.10	4.20	6.30	8.41
20,000	2.80	5.60	8.41	11.21
25,000	3.50	7.01	10.51	14.01
30,000	4.20	8.41	12.61	16.81

T2 · Muriatic acid to lower TA by 10 ppm (fl oz)

Identical to the pH calculator's T1 by construction — both tables call muriaticDoseMl() from the shared acidbase.ts. One engine, two doors.

fl oz of muriatic acid required to lower total alkalinity 10 ppm, by pool size and strength
Pool size (gal)	31.45% (20° Bé)	28.3%	14.5% (low-fume)
5,000	12.8	14.5	30.0
10,000	25.6	28.9	60.0
15,000	38.4	43.4	90.1
20,000	51.2	57.8	120.1
25,000	63.9	72.3	150.1

T3 · Reagent-selection quick table

The §4.4 reagent vectors as data — what to reach for given where pH and TA actually are. Typical band 80–120 ppm.

Reagent selection by which value is off
Your situation	Reach for	Why
TA low · pH okay	Baking soda	Raises TA strongly, pH barely
TA okay · pH low	Soda ash / aerate	pH up without over-raising TA
Both low	Baking soda first, then reassess	Baking soda often nudges pH up enough on its own
TA high · pH any	Acid + aerate	Only acid lowers TA; aerate to reclaim pH
TA inside 80–120	Nothing — leave it	Don't chase the middle of the range

All three tables released under CC BY 4.0. Attribute PoolSolver and link back.

Sources & methodology

Same engine as the pH calculator, same sourcing discipline as every page on this site. Here's where each piece comes from.

Alkalinity titration and the CaCO₃-equivalent basis trace to Standard Methods for the Examination of Water and Wastewater (APHA) — the same source family every chemistry page on this site uses for ppm definitions. 50.04 ppm CaCO₃ = 1 meq/L is the textbook number.

Carbonate buffering chemistry — why baking soda barely moves pH while strongly raising TA, why aeration off-gasses CO₂ and raises pH alone, why acid drops both at once — comes from Stumm & Morgan, Aquatic Chemistry. The canonical primary reference for natural-water carbonate equilibria.

NaHCO₃ formula weight (84.007 g/mol), NaHSO₄ MW (120.06), HCl density and normality tablecome from the CRC Handbook. The retail product purity for sodium bicarbonate is ~99% — we don't apply a purity divisor at the homeowner dose scale because the ~1% gap sits well below dosing precision.

Target bands(TA 80–120 typical) are PHTA/APSP industry conventions, not laws. The CDC Model Aquatic Health Code names a public-pool range; we don't publish that specific number here until the MAHC PDF is verified — same "verified or omitted" discipline as the chlorine page F13.

Dry-acid sulfate thresholdis intentionally absent. The agreed numbers vary across sources and manufacturers; that threshold stays off the page until a citable industry-consensus source lands. The accumulation direction is well-established — the absolute ppm at which it becomes a real problem is the part we can't source cleanly yet.

Acid safety ships unconditionally — never mix acid with chlorine, always add acid to water, dose into return flow. The wording does not soften pending citation work, mirroring the pH page exactly.

The honesty paragraph (same as the pH page, on purpose)

The dose to raise TA and the dose to lower TA are precise — pure stoichiometry, no temperature dependence, no CO₂ dependence. The final pH after dosing is not precise because it depends on CO₂ and aeration we cannot estimate from a form field. We give you direction and mechanism; we refuse to give you a decimal final pH because that would be a lie. Every calculator that does is guessing.

The shared engine. Both dosing paths (RAISE via bakingSodaTaRaiseLb, LOWER via muriaticDoseMl / dryAcidDoseLb) live in lib/dosing/acidbase.ts. The pool pH calculator imports the same functions; the alkalinity calculator's LOWER dose is asserted at build time to equal the pH calculator's for identical inputs. Drift is impossible by construction.

The forward link. Total alkalinity is one of the four primary inputs to the Langelier Saturation Index (LSI). When the LSI calculator ships it will consume this number directly — same bands, same equivalents — through the shared engine. Until then, LSI lives as prose on this page rather than a broken link.

Frequently asked questions

How much baking soda do I need to raise my pool's alkalinity?

~1.40 lb of baking soda raises TA by 10 ppm per 10,000 gallons. Multiply by ΔTA ÷ 10 and your gallons ÷ 10,000 for any other case — or just use the calculator above. Always broadcast across the surface with the pump running; don't dump in one spot.

Baking soda or soda ash — which one raises alkalinity?

Baking soda. They're different vectors: baking soda is mostly TA effect with a tiny pH nudge; soda ash is a big pH push with TA as a side effect. Reach for soda ash only when pH is also low; reach for baking soda when alkalinity is the actual problem.

Does baking soda raise pH too?

A little — direction only, not a decimal. Bicarbonate buffers near pool pH, so it nudges pH gently upward (toward the high-7s) without spiking it. We don't predict a final pH from a baking-soda dose because the result depends on CO₂ off-gassing we can't estimate from a form field.

How do I lower alkalinity without lowering pH?

You can't avoid the dip — acid hits both at once. But you can put pH back for free afterwards. Dose acid to your TA target (pH will dip temporarily); then aerate — returns up, fountains and jets on. CO₂ off-gasses and pH climbs back while TA stays at its new lower level. Acid down, air up. The pH side of the same move lives on the pool pH calculator.

What should my pool's total alkalinity be?

Conventions: 80–120 ppm typical (60–180 acceptable). Salt-cell pools and plaster surfaces often run the low end (60–80). Vinyl and fiberglass tolerate the high end. PHTA/APSP industry consensus; the CDC MAHC names a public-pool number we don't publish until the PDF is verified.

Is "alkalinity increaser" just baking soda?

Almost always yes. Branded "alkalinity up," "TA increaser," "alkalinity plus" — read the back panel and the active ingredient is overwhelmingly sodium bicarbonate. Same chemical, often a markup over plain baking soda. The dose math is identical.

Why does my alkalinity keep dropping?

Acid additions (trichlor tabs deposit acid as they dissolve, cal-hypo + low-pH water nibbles at it, muriatic doses obviously), CO₂ loss from aeration, rain dilution, splash-out, and partial-drain refills with low-TA fill water. There's no universal monthly drop rate to publish — your pool's number is your number. Measure it for a few weeks and you'll see your pattern.

How are pH and alkalinity related?

Total alkalinity is the buffer — the reservoir depth — and pH is the ball sitting on the surface. Strong alkalinity holds pH steady against inputs; weak alkalinity lets pH swing on every event. The pool pH calculator flips the camera around: there, pH is the symptom and TA is the hidden cause; here, TA is the lever and pH is what moves.

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