Pool Alkalinity Too Low: How to Fix It
Ideal total alkalinity is 80-120 ppm; below 80 is low, below 60 causes problems fast. Alkalinity buffers pH — when it's low, pH bounces unpredictably, metal fixtures corrode faster, and swimmers get eye/skin irritation.
Common causes: heavy rain, using acid to lower pH without rebalancing, and trichlor tablets gradually pulling alkalinity down.
Fix with sodium bicarbonate (baking soda) — but dose based on your exact gallons and how far below 80 ppm you are, not "a box." If raising it a lot, split into two doses 6+ hours apart.
Keep it stable: test weekly, rebalance after any pH-lowering treatment, and expect to top it up periodically if using trichlor tablets.
## Real-world example: low alkalinity, low pH, and low chlorine
Scenario: a 30,000-gallon pool with a sand filter. Starting readings: pH 6.7, Total Alkalinity 50 ppm, Free Chlorine 0.8 ppm.
Adjust alkalinity and pH together — soda ash raises pH and nudges alkalinity up too, so add it first, circulate 4–6 hours, then retest before finalizing your baking soda dose.
1. **pH:** raise from 6.7 toward a target of ~7.5 using soda ash (sodium carbonate), added separately from the baking soda: approximately 4.5 lb (72 oz) for this pool (based on ~6 oz per 10,000 gallons raising pH by about 0.2). Note that soda ash also raises TA somewhat, so add it first, circulate 4–6 hours, and retest before finalizing the baking soda amount. 2. **Total Alkalinity:** raise from 50 ppm toward a target of ~90 ppm (a 40 ppm increase) using sodium bicarbonate (baking soda): approximately 18 lb for this 30,000-gallon pool (based on ~1.5 lb per 10,000 gallons per 10 ppm increase). 3. **Free Chlorine:** raise from 0.8 ppm toward a target of ~2.5 ppm (a 1.7 ppm increase) using 10% liquid chlorine: approximately 51 fl oz (about 1.6 quarts) for this pool (based on ~10 fl oz per 10,000 gallons per 1 ppm increase). If using 65% cal-hypo granular instead, approximately 10 oz.
Safety first: these are rule-of-thumb estimates that vary by exact product concentration (check the label), pool surface type, water temperature, and cyanuric acid level. Add chemicals one at a time (never mix products together directly), keep the pump circulating, and retest between additions rather than dosing everything all at once.
Pool Balance's free calculator tells you exactly how much baking soda to add to land in the 80-120 ppm range.