Total alkalinity buffers pH in hot tubs and pools. Hold TA at 80-120 ppm, correct it before pH, and raise it with sodium bicarbonate. UK dosing guide.
Total alkalinity (TA) is important because it is the buffer that holds your pH steady. Keep TA at 80–120 ppm and pH stays in the 7.2–7.6 band where your sanitiser works and the water feels comfortable; let TA drop and pH bounces wildly after every bathe, while high TA locks pH up high where chlorine loses its power and scale forms. Always correct alkalinity first, then pH, then sanitiser.
TA measures the dissolved bicarbonates and carbonates that neutralise acids as they enter the water. Every bather, every dose of sanitiser and even rain shifts the water's acid balance; alkalinity absorbs those shifts so pH drifts slowly instead of lurching. With TA in range, a weekly test-and-tweak routine keeps everything stable. With TA too low, pH "bounces" – readings swing between acidic and alkaline day to day, corroding heaters, stinging eyes and making sanitiser levels impossible to hold. With TA too high, pH sticks stubbornly above 7.8, chlorine efficiency collapses, water clouds and scale builds on the shell and heater.
Test 2–3 times a week with 6-in-1 test strips and always adjust in the right order: alkalinity, then pH, then sanitiser. Because alkalinity is the foundation, changing it moves pH too – which is why doing it backwards wastes chemicals.
Raise TA with total alkalinity increaser (sodium bicarbonate). Dose with the pump running, wait a few hours (or overnight), retest and repeat in small steps until you reach 80–120 ppm. TA increaser nudges pH only gently, which is exactly what you want when pH is already close to range.
Lower TA with pH & alkalinity reducer (sodium bisulphate), added in small doses with the jets running. Reduce gradually over a few sessions rather than in one big dose – TA and pH fall together, and overshooting leaves you correcting in both directions. Our full total alkalinity guide for hot tubs has exact step-by-step dosing, and if pH and alkalinity are both stuck high, see high pH and alkalinity in your hot tub.
Baking soda is chemically similar, but food-grade bicarbonate gives you no water-treatment dosing instructions, no guaranteed purity for spa use, and no support if things go wrong. A spa-grade TA increaser costs little more, doses predictably, and its label tells you exactly how much to add per 1,000 litres for the rise you need.
TA is often confused with calcium hardness. Alkalinity is about carbonates buffering pH; hardness is about dissolved calcium protecting surfaces and preventing foam. They are tested and adjusted separately – low hardness in soft-water areas is corrected once per water change with a calcium hardness increaser. For how all four parameters interact, see the spa water balance essentials guide.
80–120 ppm. In that range alkalinity buffers pH so it drifts slowly and predictably; outside it, pH either bounces (low TA) or locks up high (high TA).
Alkalinity first, always. Alkalinity is the buffer that controls how pH behaves, and alkalinity products move pH as a side effect – correcting pH first just gets undone.
pH becomes unstable and tends acidic: water stings eyes and skin, metal parts and heater elements corrode, and sanitiser readings become erratic because every small addition swings the pH.
Slightly. Sodium bicarbonate raises TA strongly but pH only gently. If both are very low, correct TA to 80–120 ppm first, retest, and only then raise pH if it is still below 7.2.