Why High Alkalinity Matters
Total alkalinity (TA) acts as a buffer for pH — it determines how stable your pH stays between service visits. But when TA climbs above 120 ppm, you get problems:
- pH keeps drifting up no matter how much acid you add
- Cloudy water from calcium carbonate falling out of solution
- Scale buildup on tile lines, salt cells, and heater elements
- Chlorine becomes less effective at higher pH levels
The ideal range for total alkalinity is 80–120 ppm for most pools. Plaster pools do best at 80–100 ppm. Vinyl and fiberglass can tolerate 100–120 ppm.
What Causes High Alkalinity?
- Source water — Many municipal water supplies have TA above 200 ppm
- Over-adding sodium bicarbonate (baking soda) when raising TA
- Fresh plaster cures — New plaster leaches alkalinity for weeks
- Using calcium hypochlorite (cal-hypo) regularly adds alkalinity over time
Two Chemicals That Lower Alkalinity
1. Muriatic Acid (Hydrochloric Acid)
The most common and cost-effective option. Pool-grade muriatic acid is typically 31.45% concentration.
Dosage: To lower alkalinity by 10 ppm in a 10,000 gallon pool, add approximately 12 oz of muriatic acid.
2. Sodium Bisulfate (Dry Acid)
Easier to handle and store, but more expensive per treatment. Common brand: pH Down.
Dosage: To lower alkalinity by 10 ppm in a 10,000 gallon pool, add approximately 12 oz of sodium bisulfate.
Dosage Chart: Muriatic Acid (31.45%)
| Pool Size | Lower TA by 10 ppm | Lower TA by 20 ppm | Lower TA by 30 ppm |
|---|---|---|---|
| 10,000 gal | 12 oz | 24 oz | 36 oz |
| 15,000 gal | 18 oz | 36 oz | 54 oz |
| 20,000 gal | 24 oz | 48 oz | 72 oz |
| 25,000 gal | 30 oz | 60 oz | 90 oz |
| 30,000 gal | 36 oz | 72 oz | 108 oz |
Step-by-Step Process
- Test your water — Get accurate TA and pH readings before adding anything
- Calculate your dose — Use the chart above or our [free pool chemical calculator](/tools/pool-chemical-calculator)
- Turn off the pump (optional) — Some pros prefer adding acid with circulation off to concentrate the effect, but it's not required
- Add acid to the deep end — Pour slowly in one area, walking the perimeter
- Run the pump for 30 minutes — Let it circulate completely
- Wait 4–6 hours — Retest before adding more
- Repeat if needed — Don't try to lower TA by more than 20 ppm in a single treatment
Common Mistakes
Mistake 1: Adding Too Much at Once
Large acid doses crash the pH below 7.0, which is corrosive to equipment. Lower TA gradually over 2–3 visits.
Mistake 2: Not Accounting for pH
Muriatic acid lowers both TA and pH. If your pH is already low (below 7.4), you may need to aerate the pool after treatment to raise pH back up without affecting TA.
Mistake 3: Testing Too Soon
Chemical reactions take time. Wait at least 4 hours after treatment before retesting, or you'll get inaccurate readings and over-correct.
The Aeration Trick
Here's a pro technique: if you need to lower TA but your pH is already good (7.4–7.6), lower both with acid, then aerate the pool to raise pH back up without raising TA. Aeration methods:
- Point return jets upward to break the surface
- Run a spa spillover
- Use a fountain or waterfall feature
- Run an air blower if available
Aeration raises pH by releasing CO2 from the water. It does not affect alkalinity.
Track Your Progress
PoolOps automatically logs water chemistry at every service stop, so you can track alkalinity trends over time and see exactly how your treatments are working.