PoolChem Tracker

Pool Chemistry Explained

Pool pH

Target range

Pool pH should stay between 7.4 and 7.8. This range balances chlorine effectiveness, swimmer comfort, and protection of pool surfaces and equipment. Outside that range, problems start fast.

Why pH matters: chlorine effectiveness

This is the headline reason pH matters. Free chlorine in your pool exists in two forms that exchange depending on pH:

• Hypochlorous acid (HOCl) — the active sanitizer. Destroys bacteria and algae efficiently.
• Hypochlorite ion (OCl⁻) — about 1/80 as effective at killing microorganisms.

The ratio between them depends almost entirely on pH:

At pH 8.0, your test kit might show FC of 3 ppm, but only about 22% of that is doing real sanitizing work. At pH 7.4, more than half of the same FC reading is the active form. Same chlorine number, very different sanitizing power.

Why pH matters: scale and surfaces

The other half of why pH matters is what it does to your pool's physical structure.

• Too low (below 7.0): Water becomes aggressive. It dissolves calcium from plaster, etches surfaces, corrodes metal heaters and ladders, and degrades vinyl liners. Low pH also irritates eyes and skin.
• Too high (above 8.0): Calcium drops out of solution and forms scale on pool walls, tile lines, and inside heaters and salt cells. Water clouds. Filter pressure climbs. Salt cells fail faster.

Both extremes are expensive. Scale and corrosion damage equipment that's not cheap to replace.

What raises pool pH

pH in most pools drifts upward over time. The biggest causes:

• CO₂ outgassing — pool water naturally loses carbon dioxide to the air. Every CO₂ molecule that leaves raises pH. This is the #1 cause of slow pH climb in most pools, and it can't be prevented entirely.
• Aeration — anything that increases the water/air interface accelerates CO₂ loss: waterfalls, return jets aimed upward, fountains, splashing kids. More aeration = faster pH climb.
• High total alkalinity (TA) — TA pushes pH up. If your TA is well above 90 ppm, expect persistent upward drift.
• Soda ash, borax, or "pH increaser" — chemicals added intentionally to raise pH.
• Salt water generators — slightly raise pH as a byproduct of generating chlorine.

What lowers pool pH

• Muriatic acid — the standard chemical for lowering pool pH. Also lowers total alkalinity as a side effect.
• Dry acid (sodium bisulfate) — alternative to muriatic acid. Safer to handle but adds sulfates to the water that accumulate over time.
• Trichlor tablets — strongly acidic (pH around 3 in solution). Continuous tablet use drives pH down along with their CYA contribution.
• CO₂ injection systems — commercial pools use these for fine pH control.
• Heavy rain on low-TA pools — diluting the buffer can drop pH temporarily.

The pH and total alkalinity relationship

You can't manage pH without thinking about total alkalinity. TA is the buffer that resists pH change. Without it, pH would swing wildly with every drop of chemical you added.

• Low TA (under 60 ppm) — pH becomes unstable. Small additions cause big swings. Common after heavy rain or over-dosing acid.
• Ideal TA (60–90 ppm) — pH is stable and responds predictably to adjustments.
• High TA (above 100 ppm) — pH keeps climbing no matter how much acid you add. The TA itself needs to come down first.

If your pH keeps rising no matter what you do, your TA is almost certainly the real problem. See pool alkalinity vs pH for the full breakdown, or how to lower pool alkalinity for the fix.

How to adjust pool pH

The right chemical depends on which direction you need to move and what your alkalinity is doing.

• To raise pH only: Use soda ash (sodium carbonate). Strong effect on pH, smaller effect on TA.
• To raise pH and TA together: Soda ash works for both. If only TA is low, use baking soda instead — it raises TA without significantly affecting pH.
• To lower pH: Muriatic acid is the standard. It lowers both pH and TA.
• To lower TA without dropping pH too far: Add acid to lower both, then aerate to bring pH back up while TA stays down.

For the full comparison of pH-up chemicals, see baking soda vs soda ash. Start with smaller doses than you think you need — overshooting pH is harder to correct than approaching gradually.