pH keeps dropping. What could be causing it?

[Eyad AlDomairy]

I’ve been noticing my pool’s pH keeps dropping every few days, even after I balance it. I use chlorine granules and keep my alkalinity in range, but the pH just won’t stay stable.
Could it be something in the water source or maybe the sanitizer I’m using?

 

[Benjamin Lewis]

It sounds like you're doing all the right things with balancing the pool and using chlorine granules, but there are a few factors that could still be affecting your pH levels. The most common causes for pH drops are high levels of chlorine or other sanitizers, especially if you’re using stabilized chlorine (like Trichlor). These sanitizers can make the water more acidic over time. Another possibility is high levels of carbon dioxide (CO2) in the pool area, which can lead to pH drops as well. If your water source has high levels of minerals, it can also affect the pH, especially if you're using well water or water that hasn't been properly filtered. You might also want to check if your alkalinity levels are in range; if alkalinity is low, the pH may drop more easily. Keep an eye on these factors, and consider testing your water more frequently to catch any imbalances early.

 

[Grace Hall]

If your pool has limited aeration, CO₂ can build up and drag down pH. Try adding small doses of soda ash after balancing alkalinity, and run your jets or waterfall an extra hour to help off-gas CO₂ naturally

 

[Michael Young]

I’ve learned that low calcium hardness can make water pull minerals from plaster and drive pH down. Adding a small dose of calcium chloride every few weeks really helped stabilize my pH.

 

[Harper Clark]

Interesting points about the CO₂ and calcium—I hadn’t really considered those. I’ve been focused on keeping alkalinity in range, but maybe something else is throwing it off. Might try running the jets longer and see if that helps. Anyone else have luck with that?

 

[Ava Wilson]

I’ve had the same issue with pH dropping even when everything else looks okay. I didn’t realize CO₂ buildup could be a factor—definitely going to try running the jets longer like Grace suggested. Do you guys think stabilized chlorine makes that big of a difference? I’ve been using it too and wondering if I should switch.

 

[Abigail Scott]

I also found that filling from a well with low source-water pH can drag my pool pH down. I pre-treat fill water with soda ash in a mixing tank stops me chasing pH drops after every top-off.

 

[Hanry Carter]

I had the same pH roller-coaster turned out my jets were chugging out CO₂ like a soda machine! I started bubbling the water with my waterfall feature for 15 minutes after balancing alkalinity and pH, and boom the pH stayed put. Feels like my pool finally stopped mood swings!

 

[Ella Robinson]

I chased a slow pH slide too TA looked fine. The twist: my “chlorine granules” were dichlor (acidic) and the floater seeped overnight. One week on liquid chlorine only stopped the drop. Maybe check the label and try a bleach-only week to isolate it?

 

[William Walker]

I totally get the pH frustration! I had the same problem last summer, and I was convinced I was doing everything right. I kept adding the right amount of chlorine granules and balancing the alkalinity, but the pH just wouldn’t hold steady. After a bit of research, I figured out that the source of my water was high in CO2, which was dragging the pH down. I added a little soda ash and started running my jets a bit longer, and things finally started to stabilize! It’s been smooth sailing since then, but I still check it more often now, just to be safe. It’s one of those things you learn by trial and error.

 

[Ibrahim Bakr]

If your pH keeps dropping even while you think alkalinity is “in range,” I’d suspect your fill or top-off water, because small frequent refills can slowly pull pH down, especially with well water or if your aeration runtime changed. I had this happen and fixed it by logging when I topped off and comparing the pH trend on days with no added water, result was it was obvious the source water was the driver. How often are you adding water each week, and what’s your source?

 

[Ethan Wells]

One thing I don’t see mentioned yet is chlorine demand from organics quietly chewing up pH over time, even when alkalinity looks “fine” on paper.

If you’re using granular chlorine, a lot of those are acidic by nature, especially dichlor. Every dose nudges pH down a bit. That alone usually isn’t dramatic, but if the pool has ongoing organic load, things like pollen, fine debris, sunscreen, or even early-stage algae you can’t see yet, chlorine is constantly oxidizing that stuff. That reaction produces acidic byproducts, so pH keeps sliding even though TA tests in range.

I ran into this when my pool looked clear but the filter was loading faster than usual. Pressure would creep up, pH would drift down every few days, and I kept blaming chemistry. Once I deep-cleaned the filter, brushed more aggressively, and ran the pump longer for a couple turnovers, the pH drop slowed way down without changing my target numbers.

So if pH keeps falling, I’d look at three things together, what type of chlorine granules you’re actually using, whether sanitizer demand is higher than normal, and whether the filter is catching more fine gunk than usual. Stable pH usually comes back once demand settles and circulation keeps up.

Have you noticed chlorine dropping faster than it used to between doses, or filter pressure rising quicker than normal?

 

[Mason Blake]

One thing that tripped me up when I had this issue was assuming “alkalinity in range” meant alkalinity was actually doing its job. Mine was technically in range, but right at the low end, so it didn’t have much buffering strength. Every small acidic input pushed pH down, and it never really recovered on its own.

What I noticed was the pattern. pH would look fine right after adjusting, then slowly slide down over a few days instead of crashing all at once. That was the clue it wasn’t a sudden problem like contamination, but a weak buffer getting worn down. Bumping alkalinity up slightly within the range, not a huge jump, just enough to give it more cushion, made the pH drift slow way down.

Another quiet factor is rainfall. A couple decent rains or frequent splash-out and refills can steadily pull pH lower even if you don’t think you’re adding much water. Once I started correlating pH drops with rain or top-offs, it made a lot more sense.

If the drop is gradual and predictable, it’s usually not one big culprit but several small acidic nudges adding up. When the buffer is strong enough, those nudges stop mattering so much.