The quick answer: you can't lower total alkalinity (TA) without lowering pH at the same time. The method that works is:
- Add acid to drop pH to about 7.2.
- Aerate the water so pH rises back up while TA stays down.
- Repeat until TA hits your target.
Each 10 ppm of TA you remove takes about 25.6 fl oz of 31.45% muriatic acid per 10,000 gallons (about 200 mL per 10,000 litres). The calculator below works out the total for your pool and the size of each safe step.
What is total alkalinity?
TA measures how much pH buffer is in the water, mostly bicarbonate. It's reported in ppm as calcium carbonate.
- Too low, and pH swings wildly with every chemical you add.
- Too high, and pH keeps rising. Bicarbonate keeps releasing carbon dioxide (CO₂) into the air, and losing CO₂ pushes pH up. More bicarbonate means faster pH rise and more acid every week.
That's why high TA usually shows up as "my pH keeps going up", not as a problem on its own.
What's the right TA for your pool?
There isn't one magic number. Common targets:
| Pool type | Typical TA target |
|---|---|
| Liquid chlorine or bleach, vinyl or fiberglass | 60–80 ppm |
| Salt water (SWG) pool | 50–70 ppm (lower slows the SWG-driven pH rise) |
| Trichlor tablets as main chlorine | 80–100 ppm (trichlor is acidic, so more buffer helps) |
| Plaster pool | Set by CSI: high enough to avoid etching (negative CSI) at your calcium level |
The real test: does your pH hold steady for several days, and is your CSI near zero? If pH climbs fast, TA is probably too high for your pool. If pH drops or bounces around, it may be too low. The CSI calculator balances TA against calcium, pH and temperature.
Step by step: lowering TA
Before you start: test pH, TA, FC and CYA. Make sure FC is at least at your normal target; you'll be running the pump a lot.
- Calculate the total acid needed for your TA drop:
(current TA − target TA) ÷ 10 × 25.6 fl oz × (your gallons ÷ 10,000).
Example: a 20,000 gallon pool going from 140 to 80 ppm.
- That is a 60 ppm drop: 308 fl oz, about 2.4 gal of 31.45% acid in total, spread over several rounds.
- Don't add it all at once.
- Add acid to bring pH down to about 7.2, and no lower. Use the pH calculator for this step's amount. If pH was high to begin with, this is your pH correction too: one acid dose, not two. Pour slowly into the deep end with the pump running.
- Aerate. Point return jets up at the surface. Run waterfalls, spillovers and fountains. Some owners use an air compressor or a leaf blower blowing into a pipe in the deep end. Aeration drives CO₂ out, raising pH without changing TA.
- When pH is back to about 7.6–7.8, retest and repeat: acid down to 7.2, aerate again.
- Retest TA every day or two. Stop when you reach target.
Depending on how far you're going and how much you aerate, this takes from a few days to a couple of weeks.
Why not just dump all the acid in? It would lower TA, but it would also crash pH far below 7.0 (adding a second acid dose "for pH" on top of the TA dose does the same: it can take pH to about 7.0), which etches plaster, can wrinkle vinyl and corrodes metal. Raising pH back with soda ash would then add the TA right back. Aeration is the free, TA-neutral way to bring pH back up.
Safety
- Wear goggles and gloves. Stand upwind.
- Never mix acid and chlorine, and wait 30 minutes between adding them.
- Don't let pH sit below 7.0. With vinyl liners, many owners stay at 7.2 or above.
- Keep heaters and salt cells off while pH is very low, if the manufacturer advises it.
What raised your TA in the first place?
- Baking soda or "alkalinity increaser" added on a store's advice.
- Fill water. Some municipal and well water arrives with TA of 150 ppm or more. If you top up a lot, TA will keep returning, and you'll need a regular acid routine.
- Cal-hypo, soda ash or "pH up" used to correct pH that was dropping for some other reason.
- Tile and plaster startup. New plaster raises pH, and correcting it is part of the startup process.
After TA is fixed
- Expect less acid overall. With TA at the right level, pH drifts up more slowly. Many owners go from adding acid every three days to once a week or less.
- Consider borates (about 50 ppm) for extra pH stability, especially in SWG pools.
- Log TA monthly. If it creeps up again, check your fill water.
Common mistakes
- Trying to lower TA with "alkalinity decreaser" and no aeration. You lower pH and TA together, then raise pH again with a product that adds TA. It's a circle.
- Lowering TA too far, below about 50 ppm in most pools, especially with trichlor, which keeps pushing pH down.
- Ignoring CSI in plaster pools. Low TA and low calcium together can etch plaster.
Do it with Pool Calc
Pool Calc works out each acid step from your TA and pool volume, reminds you to aerate and retest, and charts TA so you can see it falling. Your custom TA target stays exactly where you set it.
One pool? Every feature, free. No account, no ads, and iCloud backup is included.
Safety
- Keep chemicals out of reach of children and pets, and keep them out of the water until it is back in range.
- Never mix chemicals. Never add acid and chlorine together: mixing them releases toxic chlorine gas.
- Add chemicals to water, never water to chemicals.
- Store chemicals sealed, cool and dry, apart from each other.
- Read and follow the product label. It always comes first.