Water Alkalinity Calculator
Dose baking soda to lift pool alkalinity to target, in liters or gallons.
What it does
Total alkalinity is the shock absorber of pool water. When it sits in range, pH holds steady and chlorine works predictably; when it sags, pH bounces and eyes sting. Raising it is a weight problem: a known volume times a known ppm gap equals a known mass of baking soda.
The tool above solves that weight. Enter volume plus current and target readings in metric or imperial. It returns the baking soda dose, the ppm rise, and the target for the log sheet. Defaults describe 50000 L moving from 60 to 100 ppm, so the page opens solved at 3.6 kg.
The factor does the quiet work. One ppm means one milligram per liter, so the pure math would be volume times rise in milligrams; the 0.0018 factor turns that into grams of boxed product with real world strength and mixing in mind. The imperial note shows the twin form (gallons times rise times 0.0068) so both modes land together: 7.94 lb for the 13209 gal mirror.
Dosing discipline matters more than arithmetic. Add a third of the computed mass with the pump running, wait hours, retest, and repeat. Alkalinity drags pH upward as it rises, so confirm pH after TA settles rather than chasing both at once. Never swim through a correction; let the water clear and test in range first.
Use the table for common pool sizes at a 10 ppm lift, then run your exact gap. The page doses sodium bicarbonate rises only and refuses a target at or below current, since lowering TA is an acid job. Spas need the same math at small volumes, so measure twice and scale down with care.
How to use
- Pick metric (L, kg) or imperial (gal, lb).
- Enter the pool volume.
- Enter current and target alkalinity in ppm.
- Read the baking soda dose and the rise.
- Add one third with the pump running, then retest.
- Repeat to target and confirm pH after.
Formula
- Volume
- Pool or spa volume: L metric, gal imperial.
- Current
- Measured total alkalinity in ppm.
- Target
- Goal total alkalinity in ppm.
- Rise
- Target minus current, must stay positive.
The 0.0018 factor converts ppm (mg/L) into baking soda weight with an allowance for product strength and mixing losses, matching the field rule of 1.5 lb per 10000 gal per 10 ppm. It assumes sodium bicarbonate only, good circulation, and no fresh dilution during dosing. To lower TA, use acid instead; this page refuses a non positive rise.
Worked example
Example: 50000 L from 60 to 100 ppm
A 50000 L pool tests 60 ppm total alkalinity with a 100 ppm target. Find the baking soda dose.
- Rise needed = 100 - 60 = 40 ppm.
- Dose = 50000 L x 40 x 0.0018 = 3600 g.
- That is 3.6 kg of baking soda.
- Imperial mirror: 13209 gal with the same rise needs 7.94 lb.
- Add in thirds with the pump running and retest.
- pH will drift up, so check pH after TA settles.
Reference table
| Pool size | Metric dose | Imperial dose |
|---|---|---|
| 25000 L (6604 gal) | 0.45 kg | 0.99 lb |
| 50000 L (13209 gal) | 0.9 kg | 1.98 lb |
| 75000 L (19813 gal) | 1.35 kg | 2.98 lb |
| 100000 L (26417 gal) | 1.8 kg | 3.97 lb |
Limits
- Sodium bicarbonate rises only; no lowering math.
- Assumes good mixing and no dilution mid dose.
- Field factor, not lab purity; retest rules.
- Spa doses need extra care at small volumes.
Common mistakes
- Dosing the whole mass at once.
- Chasing pH before TA settles.
- Mixing liters with the gallon factor.
- Targeting above 120 ppm for most pools.
- Testing within minutes instead of hours.
Try it yourself
Quick checks. Answers sit tucked under each question.
25000 L from 70 to 90 ppm?
Rise 20 ppm. Dose 0.9 kg of baking soda.
100000 L from 50 to 120 ppm?
Rise 70 ppm. Dose 12.6 kg of baking soda.
40000 L from 80 to 110 ppm? Work it by hand.
Volume 40000 L, rise 30 ppm: 40000 x 30 x 0.0018 = 2160 g = 2.16 kg.
Questions
What is total alkalinity?
The water buffer that resists pH swings, read in ppm. Pools usually target 80 to 120 ppm so sanitizer works steadily.
What chemical does the tool dose?
Sodium bicarbonate (plain baking soda). About 0.0018 g per liter per ppm here, which matches 1.5 lb per 10000 gal per 10 ppm.
Why add in thirds?
Add a third, run the pump, retest after several hours, then repeat. Dumping all at once overshoots and clouds water.
Does it work in gallons and pounds?
Yes. Pick imperial and enter gallons: 13209 gal from 60 to 100 ppm needs 7.94 lb.
How do I lower alkalinity?
Use acid (muriatic or dry) in small steps with air running, and retest. This page doses rises only.
Should I retest pH after?
Yes. TA and pH move together, so confirm pH after TA lands and adjust sanitizer with fresh readings.