Total alkalinity is the setting that keeps pH stable. Get it right and pH stops bouncing. Get it wrong and you will be adding acid every few days.
This guide shows the target range, and how much baking soda to add to a pool measured in litres.
What Should Pool Alkalinity Be?
Aim for 80 to 120 ppm total alkalinity. For marbelite and plaster pools, the upper half of that range works best.
Below 80 ppm the pH swings on its own. Above 120 ppm the pH locks high and the water starts to scale.
How Much Baking Soda to Add to a Pool
Sodium bicarbonate is the standard way to raise alkalinity. It is sold as baking soda or as alkalinity increaser. Both are the same chemical.
The working figure is 180 g of baking soda per 10,000 litres raises total alkalinity by about 10 ppm.
That number comes from the widely used benchmark of 1.5 lb per 10,000 US gallons, converted to litres. It lines up across independent sources.
Pool Alkalinity Dosing Chart in Litres
| Pool volume | Raise 10 ppm | Raise 20 ppm | Raise 40 ppm |
|---|---|---|---|
| 20,000 L | 360 g | 720 g | 1.44 kg |
| 30,000 L | 540 g | 1.08 kg | 2.16 kg |
| 40,000 L | 720 g | 1.44 kg | 2.88 kg |
| 50,000 L | 900 g | 1.8 kg | 3.6 kg |
| 60,000 L | 1.08 kg | 2.16 kg | 4.32 kg |
Most Cape Town family pools sit between 30,000 and 50,000 litres. If you do not know yours, measure it before dosing.
How to Raise Alkalinity in a Pool Without Spiking pH
Baking soda nudges pH up a little as it raises alkalinity. That is normal.
Add it with the pump running. Broadcast it across the deep end. Wait six hours, then retest.
Never add more than about half the calculated dose at once. Overshooting alkalinity is far harder to fix than undershooting it.
How to Lower Pool Alkalinity
Use hydrochloric acid, sold locally as pool acid. Add it in a narrow stream in one spot with the pump off, let it sit briefly, then run the pump.
This drops pH as well as alkalinity. Aerate afterwards to bring pH back up while alkalinity stays down.
Pool Alkalinity and pH: Which to Fix First
Alkalinity first, every time. pH will not hold until alkalinity is in range.
Chasing pH while alkalinity sits at 40 ppm wastes chemicals. You correct it, and days later it has moved again.
What Pushes Pool Alkalinity Out of Range in Cape Town
- Borehole and wellpoint top-ups, which often run high in alkalinity
- Winter rain diluting the pool, which drops it
- Heavy acid dosing after a green pool recovery
- Salt chlorinators, which drive pH up over time
Signs Your Pool Alkalinity Needs Attention
- pH will not stay put between weekly tests
- Chalky scale forming on the waterline and steps
- Eye irritation despite chlorine reading normal
- Chlorine burning off faster than it should
How Much Baking Soda to Raise Alkalinity in a Pool by 20 ppm
On a 40,000 litre pool you need about 1.44 kg. On a 50,000 litre pool it is about 1.8 kg. Work from your own measured volume, not an estimate.
Pool Alkalinity Calculator: Sodium Bicarbonate Needed
Sodium bicarbonate and baking soda are the same thing. Alkalinity increaser sold in pool shops is also sodium bicarbonate, usually at a higher price per kilogram.
Get Your Pool Alkalinity Tested in Cape Town
Dosing works when the starting reading is right. A cheap strip that is six months old will send you in the wrong direction.
Our team tests water on site across Cape Town and the Winelands. We balance the pool properly and tell you what it actually needs, not what a generic chart says. Request a free quote or browse our pool maintenance services.
