The Real Culprit — Total Alkalinity
Most pool owners reach for muriatic acid the moment pH climbs above 7.6. It works — temporarily. But if your total alkalinity (TA) is above 120 ppm, pH will bounce right back up within 24–48 hours. Every. Single. Time.
Here's why: total alkalinity is essentially a pH buffer. Its job is to resist pH changes. At high levels, TA continuously pushes pH upward, fighting any acid you add. Lowering pH without first addressing high TA is like bailing water from a leaking boat — you'll never win.
Total Alkalinity (TA)
Acts as a pH buffer. High TA (above 120 ppm) constantly drives pH upward, resisting acid corrections.
CO₂ Outgassing
Aeration (jets, waterfalls, splashing) drives CO₂ out of water. As CO₂ leaves, pH climbs naturally.
Salt Chlorination
Salt cells produce sodium hydroxide as a byproduct — a highly alkaline compound that steadily raises pH.
| Total Alkalinity Level | pH Stability | Action Needed |
|---|---|---|
| Below 60 ppm | pH swings wildly (too low) | Add sodium bicarbonate |
| 80–100 ppm ✅ | Stable, ideal range | Maintain here |
| 100–120 ppm | Mild upward drift | Minor acid dose |
| Above 120 ppm | Constant pH rise | Targeted TA reduction |
CO₂ Outgassing Explained
Water naturally contains dissolved carbon dioxide (CO₂). When CO₂ is present, it forms carbonic acid, which keeps pH slightly lower. When CO₂ escapes — through splashing, waterfalls, jets, or even wind across the surface — that acidic compound disappears and pH rises.
This is a completely natural chemical process. Every pool experiences some CO₂ outgassing. The problem arises when high TA amplifies the effect. At high alkalinity levels, the carbonate buffering system actively pulls CO₂ out of solution faster, accelerating the pH rise.
Other Causes of Rising Pool pH
Beyond high TA and outgassing, a few other factors can contribute to persistent pH rise:
- Salt chlorination: Salt cells electrolyze water to produce chlorine, and a byproduct of this process is sodium hydroxide — an alkaline compound. Saltwater pools almost universally trend toward higher pH and typically need weekly acid additions.
- Bather load: Body oils, sweat, sunscreen, and cosmetics are slightly alkaline. Heavy use (pool parties, hot weather swims) can contribute to gradual pH rise.
- Sanitizer type: Trichlor tablets are acidic and actually help buffer pH downward. If you switch from trichlor to dichlor (which is pH-neutral to slightly high) or liquid chlorine, you may notice more pH drift.
- New plaster or concrete: Freshly plastered pools leach calcium carbonate for weeks, which raises both pH and calcium hardness dramatically.
The Fix — Lower Total Alkalinity First
The only permanent solution to chronic pH rise is getting total alkalinity into the correct range: 80–100 ppm. Once TA is controlled, pH becomes manageable and you'll only need small, infrequent adjustments.
The trick to lowering TA without over-crashing pH is called targeted acid dosing:
- Add muriatic acid to one concentrated spot in the deep end with the pump off
- Let it sit for 1 hour, then turn pump on
- The acid aggressively attacks alkalinity in the concentrated zone
- Turn on aeration (jets, waterfall, fountain) overnight to outgas CO₂ and allow pH to naturally rise back
- Retest the next morning — TA will be lower, pH recovers on its own
- Repeat over several days until TA reaches 80–100 ppm
Step-by-Step Process to Stop pH from Rising
Test Total Alkalinity and pH
Use a reliable test kit (not just test strips). Record both numbers. If TA is above 120 ppm, that's your primary target.
Calculate Your Acid Dose
Use a pool calculator to determine how much muriatic acid brings TA to 80–100 ppm. Don't try to do it all in one dose — split it over 2–3 days.
Targeted Acid Dose (Pump Off)
Turn off pump. Pour acid in one spot at the deep end. Wait 1 hour. Turn pump on low to circulate. pH will drop significantly.
Aerate Overnight
Run jets, waterfall, or fountain overnight to outgas CO₂. pH will naturally rise back toward 7.4–7.6 without affecting TA.
Retest the Next Morning
Test TA and pH. TA should be lower. If still above 100 ppm, repeat steps 3–4. Each cycle brings TA down further.
Maintain at 80–100 ppm TA
Once TA is in range, pH will stabilize. For saltwater pools, expect to add a small acid dose weekly — that's normal and manageable.
How Much Acid Do You Actually Need?
The amount of muriatic acid needed depends on your pool size and current TA level. As a rough guide for a 20,000-gallon pool:
- To lower TA from 150 → 100 ppm: approximately 3–4 quarts of 31.45% muriatic acid (split over multiple doses)
- To lower TA from 120 → 100 ppm: approximately 1.5–2 quarts
- Always use a pool calculator for your exact volume — over-dosing can crash pH below 7.0 and cause corrosion