Subject: pH Rose After Muriatic Acid Addition (Confused by the Outcome)
Hi Everyone,
I recently did a drain and refill and have been balancing the chemical myself following TFP protocol. I got FC, CYA and Salt where I want it and I am now working on reducing my TA. I’ve been carefully following the PoolMath calculator to estimate how much muriatic acid to add, lowering pH and TA in stages. However, I’m seeing outcomes that don’t match what the app predicts (especially regarding pH drop), and I’m not sure what’s going on.
Here are the details from yesterday (12:30 PM) sample taken on the deep end, elbow deep:
Following PoolMath’s recommendation, I added 32 oz of 31.45 percent HASA muriatic acid (purchased from Leslie’s) with a target pH of 7.3. I diluted it to about 1.85 percent in softened water and slow-dripped it over two hours directly into agitation created by using an aquarium wave maker (this was mostly out of caution). I’m a bit paranoid about plaster etching and don’t have a strong return jet (due to my in-floor cleaning system). This setup lets me avoid having to brush aggressively right after acid addition and allows me to walk away until it's done.
I got pool gallons size directly from builder and it adds up with how much salt and CYA I have been needing to reach my target.
I didn’t actively aerate using water features (such as spa spillover or fountains), but I do run my pump continuously 24/7. The in-floor system does trigger a spillover when it cycles the spa, and I have a fairly large shallow beach section that creates surface agitation when its zone is active.
This morning at 9:30 AM (less than 24 hours later), I retested and to my surprise, pH had actually risen to 7.87 (instead of dropping to the expected 7.3).
the drop ph test is actually a little darker than the 7.8 mark (see picture).
Pool was built in 2021 and did acid was a few weeks ago if it makes a difference.
I’m scratching my head. The only semi-scientific explanation I can come up with is this:
Even though I used the full acid dose, the slow, diluted addition might have allowed CO₂ to off-gas in real time due to agitation. This may have counteracted the acid’s immediate effect on pH. So the H+ ions still reacted with carbonates (which would explain why my TA dropped), but the pH rebound happened much faster than expected.
The silver lining is that my TA did drop as expected to about 115 (11th drops brings solution from greyish green to light pink and it gets dark pink at 12th drop), so I know the acid wasn’t fake (otherwise I’d be wondering if Leslie’s sold me dog pee instead of muriatic acid).
Any thoughts? Has anyone else seen this kind of pH behavior when using a slow-drip method?
Thank you all!
Full pool specs are in my signature
Hi Everyone,
I recently did a drain and refill and have been balancing the chemical myself following TFP protocol. I got FC, CYA and Salt where I want it and I am now working on reducing my TA. I’ve been carefully following the PoolMath calculator to estimate how much muriatic acid to add, lowering pH and TA in stages. However, I’m seeing outcomes that don’t match what the app predicts (especially regarding pH drop), and I’m not sure what’s going on.
Here are the details from yesterday (12:30 PM) sample taken on the deep end, elbow deep:
- FC: 7.5
- pH: 7.83 (confirmed with two calibrated pH meters and a drop test)
- TA: 125
- CYA: approximately 67 (based on drop test)
- Calcium: 350 ppm
- Temp: 66°F
- Salt: 3650 ppm
Following PoolMath’s recommendation, I added 32 oz of 31.45 percent HASA muriatic acid (purchased from Leslie’s) with a target pH of 7.3. I diluted it to about 1.85 percent in softened water and slow-dripped it over two hours directly into agitation created by using an aquarium wave maker (this was mostly out of caution). I’m a bit paranoid about plaster etching and don’t have a strong return jet (due to my in-floor cleaning system). This setup lets me avoid having to brush aggressively right after acid addition and allows me to walk away until it's done.
I got pool gallons size directly from builder and it adds up with how much salt and CYA I have been needing to reach my target.
I didn’t actively aerate using water features (such as spa spillover or fountains), but I do run my pump continuously 24/7. The in-floor system does trigger a spillover when it cycles the spa, and I have a fairly large shallow beach section that creates surface agitation when its zone is active.
This morning at 9:30 AM (less than 24 hours later), I retested and to my surprise, pH had actually risen to 7.87 (instead of dropping to the expected 7.3).
the drop ph test is actually a little darker than the 7.8 mark (see picture).
Pool was built in 2021 and did acid was a few weeks ago if it makes a difference.
I’m scratching my head. The only semi-scientific explanation I can come up with is this:
Even though I used the full acid dose, the slow, diluted addition might have allowed CO₂ to off-gas in real time due to agitation. This may have counteracted the acid’s immediate effect on pH. So the H+ ions still reacted with carbonates (which would explain why my TA dropped), but the pH rebound happened much faster than expected.
The silver lining is that my TA did drop as expected to about 115 (11th drops brings solution from greyish green to light pink and it gets dark pink at 12th drop), so I know the acid wasn’t fake (otherwise I’d be wondering if Leslie’s sold me dog pee instead of muriatic acid).
Any thoughts? Has anyone else seen this kind of pH behavior when using a slow-drip method?
Thank you all!
Full pool specs are in my signature
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if you’re TA is that high then it’ll make the oh rise faster. Don’t wait 24 hours to test next time.