Total alkalinity is one of those pool chemistry concepts that sounds complicated but is actually pretty simple once you understand what it does. If you've ever adjusted your pH only to have it bounce back a day later, low alkalinity is almost certainly the reason why.
Think of alkalinity as a buffer for your pH. It resists changes in pH — keeping it from swinging wildly up or down. When alkalinity is in range (80-120 ppm), pH stays relatively stable. When it's too low, pH becomes erratic and hard to control.
Low alkalinity also makes water corrosive — it can etch plaster, corrode metal fittings, and irritate swimmers' eyes and skin.
The product you want is sodium bicarbonate — which is literally baking soda. Pool stores sell it as "alkalinity increaser" at a significant markup, but it's the exact same thing. Buy a big box of baking soda from a warehouse store and save money.
As a general rule, 1.5 lbs of baking soda raises alkalinity by about 10 ppm in a 10,000 gallon pool.
| Pool Size | Raise 20 ppm | Raise 40 ppm |
|---|---|---|
| 10,000 gal | 3 lbs | 6 lbs |
| 15,000 gal | 4.5 lbs | 9 lbs |
| 20,000 gal | 6 lbs | 12 lbs |
| 25,000 gal | 7.5 lbs | 15 lbs |
💡 Add it in increments. Add half the calculated amount, wait 4-6 hours with the pump running, then retest. It's much easier to add more than to deal with alkalinity that's too high.
⚠️ Fix alkalinity before pH. Alkalinity affects pH — if you adjust pH first and alkalinity is off, pH will drift right back out of range. Always balance alkalinity first, then pH.
High alkalinity (above 120 ppm) causes pH to creep up and makes it hard to lower. To reduce alkalinity, add muriatic acid in small amounts with the pump running. The same acid that lowers pH also lowers alkalinity — it just depends on how much you add and how you add it.
Tell Wade your alkalinity reading and pool size and he'll tell you precisely how much baking soda to add. No math required.
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