Calculate how much muriatic acid to lower pool pH, or how much soda ash to raise it. Target range: 7.4–7.6.
pH is the single most important number in pool chemistry — it controls how effectively chlorine sanitizes your water, how comfortable the water feels, and whether the water is eating your pool or depositing scale on it.
At pH 7.5, roughly 50% of your free chlorine is in the active HOCl form. At pH 8.0, that drops to about 22%. You can have a "correct" chlorine reading and still have ineffective sanitation if pH is too high.
Muriatic acid (hydrochloric acid, HCl) is the standard product for lowering pool pH. It reacts quickly and leaves no residue. Two common strengths are available:
The dose depends on both the pH drop needed and your total alkalinity (TA). Higher TA means stronger buffering, so the same pH change requires more acid. The calculator accounts for this — enter your TA for the most accurate result. Leaving it blank uses 80 ppm as a default.
Pre-dilute in a bucket of pool water before adding. Pour acid into water, never water into acid. Wear eye protection and gloves. Add near a return jet with the pump running. Never mix with chlorine or other chemicals.
Soda ash (sodium carbonate, Na₂CO₃) is the correct product for raising pH. It acts quickly and has a pronounced effect on pH relative to the amount used — much stronger than baking soda, which primarily raises alkalinity.
A standard dose of 6 oz raises pH by about 0.2 units in 10,000 gallons. For large increases, split into multiple smaller doses and retest after each — soda ash can temporarily cloud the water and it's easy to overshoot.
Baking soda (sodium bicarbonate) raises total alkalinity — it has very little effect on pH. Soda ash (sodium carbonate) raises pH. They look similar and are sometimes confused, but they do different jobs. Check the label: "sodium bicarbonate" for TA, "sodium carbonate" for pH.
This is one of the most common pool chemistry problems. The cause is almost always high total alkalinity. When TA is above 100–120 ppm, it acts as a one-way pH pump: it buffers against pH drops (requiring lots of acid), but CO₂ continuously escapes through aeration — jets, waterfalls, splashing — which drives pH upward. The result is that you add acid, pH drops briefly, then climbs back up within days.
The real fix: lower TA to 60–80 ppm using muriatic acid in the TA-lowering mode, then aerate to bring pH back to 7.4–7.6. Once TA is in range, pH stabilizes and needs only occasional small adjustments.
7.4–7.6 is the target for most pools. This range optimizes chlorine effectiveness, is comfortable for swimmers (matching the pH of human eyes and mucous membranes), and keeps water balanced — neither corrosive nor scaling.
pH naturally drifts upward in most pools due to CO₂ off-gassing through aeration (jets, waterfalls, splashing), the electrolysis process in saltwater pools, and liquid chlorine additions (which are alkaline). High total alkalinity amplifies the drift. If pH keeps rising despite regular acid additions, lowering TA is the durable fix.
No — baking soda (sodium bicarbonate) raises total alkalinity, not pH. To raise pH, use soda ash (sodium carbonate). The products are completely different despite looking similar. If your pH is low and TA is also low, start with baking soda to bring TA to 80–100 ppm — a stable TA helps pH self-correct. If TA is already in range, use soda ash to raise pH directly.
Wait at least 30 minutes with the pump running after adding muriatic acid or soda ash, then retest pH before allowing swimmers. For large acid additions (over 1 quart), wait at least 1 hour. The chemical is highly concentrated near the addition point until circulation distributes it throughout the pool.
High total alkalinity is almost certainly the cause. When TA is above 120 ppm, the pool acts as a continuous pH-raising machine — aeration drives CO₂ off faster than it can equilibrate, and the alkalinity buffers any acid you add. Use the muriatic acid calculator in TA-lowering mode to bring TA to 60–80 ppm. After that, aerate to recover pH. Once TA is in range, pH becomes far more stable.
PoolChem Tracker calculates your acid or soda ash dose automatically from your logged pH and TA readings — no manual lookup needed. It also shows your pH trend over time so you can catch drift early.
