Alkalinity calculator
Add about 6.8 lbs of baking soda (sodium bicarbonate) to raise TA by 30 ppm. Add in thirds, circulating and retesting between.
Treat this as a starting dose: add less than the full amount when unsure, circulate for a few hours, retest, repeat. Always follow your product's label.
Low total alkalinity is why pH gets weird — bouncing high then low from small additions or a rainstorm, refusing to hold anywhere. Alkalinity is the buffer that keeps pH stable, so when it's low, fix that first and pH stops misbehaving. Here's how. Follow product labels and confirm your volume.
Why low alkalinity causes chaos
Total alkalinity (TA) buffers the water against pH swings. When TA falls below about 80 ppm, that buffer weakens and pH becomes volatile — it can crash or spike from a small dose of chemical, a heavy rain, or even a busy swim day. Low TA can also make the water corrosive, etching plaster and attacking metal equipment. So erratic, unpredictable pH readings usually trace back to alkalinity that's too low to hold anything steady. Raise the buffer and the chaos stops.
Confirm it's actually low
Test to be sure. Check TA and pH together; the target for most pools is roughly 80–120 ppm. If TA reads below that and pH swings around unpredictably, low alkalinity is your culprit. Note your pool volume so you can dose accurately. As always, retest rather than acting on one reading, and check whether recent heavy rain or a big top-off with low-alkalinity fill water explains the drop.
Raise TA with baking soda
You raise alkalinity with sodium bicarbonate — baking soda, sold as an alkalinity increaser. It's forgiving: it raises TA well and nudges pH up only slightly, so it's hard to overdo. Broadcast the measured amount across the surface (or dissolve and pour it) with the pump running, let it circulate for several hours, and retest. If you have a lot to make up, add in stages and retest between rounds rather than dumping one huge dose. Because bicarb is gentle, this rarely overshoots.
Then tidy up pH
Fix the buffer, then the pH. Raising TA lifts pH a little, so once alkalinity sits in the 80–120 ppm band, retest pH and nudge it into the 7.2–7.6 range if needed. Do it in that order — alkalinity first, pH second — and you'll stop chasing the two around each other. Once both hold across a couple of tests, your chemistry is stable and far less fussy week to week. Our alkalinity calculator sizes the bicarb dose from your volume and reading.
Stop it from dropping again
Address recurring lows. Frequent heavy rain, lots of fresh fill water, or repeated acid additions to lower pH can all erode alkalinity over time. If TA keeps sliding, stay ahead of it with routine bicarb top-ups and watch your fill water's alkalinity. Keeping the buffer in range is the single best thing you can do to make pH — and everything downstream of it — behave.
Frequently asked questions
What happens if pool total alkalinity is too low?
Low total alkalinity can make pH swing more easily, which can make water harder to balance and less comfortable for swimmers.
How do you raise low alkalinity in a pool?
Use an alkalinity increaser or sodium bicarbonate according to the product label and your pool volume. Add it in stages, circulate, and retest before adding more.
Does baking soda raise pool alkalinity?
Yes, sodium bicarbonate is commonly used to raise total alkalinity. It can affect pH too, so dose gradually and retest.
Can low alkalinity make pH drop?
Low alkalinity can make pH less stable, so pH may move more easily after rain, acid additions, sanitizer use, or swimmer load.
Should I raise pH or alkalinity first?
If total alkalinity is very low, correct alkalinity first in small steps, then fine-tune pH after the water circulates and stabilizes.
