pH Won’t Go Up No Matter What You Add? Check Alkalinity First

My sister texted me a photo of her test kit one May morning with a single word: “Why?” Her pool in Colorado had just been opened. The pH tube was the palest yellow it could be. She had added soda ash twice that week. Each time, the pH crept up for a day and then slid right back down.

I asked one question: “What’s your alkalinity?” She had not tested it. When she did, it read about 40 ppm. Her chlorine tablets, a rainy spring and a winter of slow drift had pulled it low. Once she raised alkalinity first, pH stopped sliding and finally stayed put. If your pH refuses to budge, here is the order that fixed hers.

Why pH refuses to stay up

pH and total alkalinity are closely linked. Alkalinity is the water’s buffer. It soaks up acids and keeps pH from swinging. When alkalinity is low, there is very little buffer. Anything acidic that enters the water pulls pH down quickly. Anything you add to raise pH gets used up just as fast.

The usual reasons pH will not hold:

• Low total alkalinity. This is the most common cause by far. Many pools need alkalinity in roughly the 80 to 120 ppm range to hold pH steady, though some setups run lower on purpose.
• Acidic chlorine tablets. Trichlor tablets are very acidic. They steadily push pH and alkalinity down. Dichlor is also mildly acidic. A floater full of tablets can work against you every day.
• Rain and runoff. Rain is often slightly acidic. A wet spring can dilute alkalinity and nudge pH down, especially in pools that get a lot of rain relative to their size.
• Too much acid earlier. An overdose of muriatic acid or dry acid can knock both pH and alkalinity low in one step.
• The wrong product for the job. Baking soda raises alkalinity a lot and pH a little. Soda ash raises pH more, and alkalinity some. Using only one when you need the other can feel like nothing is working.
• A testing problem. High chlorine can bleach some pH indicators and give false readings. Old reagents and strips past their date can also mislead you.
• Automation set too low. If you have an acid feeder or pH controller, its setpoint may be lower than you think. It will keep adding acid as you try to raise pH.

The fix, in order

Test first, add chemicals second. That saying matters more here than anywhere, because it is easy to keep adding pH increaser and never touch the real cause.

1. Confirm your pH reading. Check that your reagents or strips are within their date. If chlorine is very high, wait for it to drop or use a kit made to read accurately at higher chlorine. Many pool stores will test a sample free, which is a good cross-check.
2. Test total alkalinity. This tells you whether you have a buffer problem. If alkalinity is low for your pool type, fix it before you chase pH. Write down both numbers and the date.
3. Raise alkalinity with baking soda in steps. Sodium bicarbonate, sold as baking soda or alkalinity increaser, raises alkalinity with only a small change in pH. Use the dosing chart on the product or a pool calculator with your pool’s volume. Add about half the calculated dose first.
4. Add it the right way. Broadcast it across the deep end or pre-dissolve it in a bucket of pool water if the label allows. Add the product to the water, never water to the product. Keep the pump running and brush any that settles.
5. Retest after six hours or more. Let the water circulate fully before testing again. Then add more baking soda if alkalinity still needs to come up. Small steps prevent overshooting.
6. Now check pH again. Often pH rises on its own once alkalinity is in range. If it is still low, use soda ash (sodium carbonate) in small doses per the label. Soda ash raises pH more strongly and can cloud the water if added too fast.
7. Use aeration as a gentle helper. Running water features, pointing returns at the surface or using an air bubbler drives off carbon dioxide. That raises pH without adding alkalinity. It is slow but free, and it is the same effect that makes my own pool’s pH climb.
8. Remove the source. If trichlor tablets are your main chlorine, consider switching some or all of your chlorine to liquid chlorine. It is close to pH-neutral over time. Check acid feeder setpoints too, and stop any acid you were adding by habit.

Read nextpH Keeps Rising in Your Pool? Why and How to Slow It

Which product raises what

This is where my sister got tripped up. She was using soda ash to fix a buffer problem. It helped pH a little, but not enough to hold. The table below shows the general difference.

Follow each product’s label for dosing. Strengths vary between brands, so a chart for one product may not match another.

Why low pH is worth fixing

Low pH can feel like a minor annoyance, but it can cause real damage over time. Water with low pH and low alkalinity tends to be aggressive toward pool surfaces and metal parts.

• Plaster can etch and become rough, and grout can wear away.
• Vinyl liners can wrinkle and age faster.
• Metal parts like heater exchangers, ladder anchors and rails can corrode. Dissolved metals can then stain the pool.
• Swimmers may notice stinging eyes or itchy skin. Anyone with a reaction that does not go away should see a medical professional.
• Chlorine is used up faster in some low pH conditions, so your sanitizer bill climbs.

Common mistakes when pH won’t rise

• Skipping the alkalinity test. This was my sister’s mistake. pH alone does not tell the whole story.
• Dumping in a huge dose of soda ash. Large doses can cloud the water and overshoot. Many labels limit how much to add at once.
• Testing right after adding product. You may be reading a mixing zone. Wait for the pump to circulate the water.
• Keeping the tablet floater full. If trichlor is the cause, adding more increaser while tablets keep dissolving is a tug of war.
• Raising alkalinity too high. Overshooting alkalinity can make pH rise too fast later. Go in steps and retest.
• Trusting expired strips. I keep a marker on my kit and write the purchase date on every new bottle.

A note for saltwater and low-alkalinity setups

Some pools run alkalinity on the lower end on purpose. Salt systems and pools with waterfalls often do this to slow upward pH drift. My own pool sits lower than my sister’s for that reason. If your equipment maker or pool builder suggests a lower alkalinity target, follow it. The goal is a range that holds pH steady in your specific pool, not one number for every pool.

If you run a lower target and pH still drops, look for acid sources. Tablets, an acid feeder or heavy rain are the usual suspects. Then raise alkalinity a little at a time until pH holds.

When to call a pool pro

• pH and alkalinity keep dropping even after you stopped using acidic tablets and acid.
• Your pool shows etching, roughness or new stains on the surface.
• You see corrosion on heater parts, ladders or rails. Heater service should go to a licensed pro, especially for gas heaters.
• An acid feeder or pH controller is not behaving as expected.
• You are unsure about dosing for a large or unusual pool. A local water lab can test and calculate doses.