Can't stabilize ph

[cdingess]

Whenever I add bleach my ph increase to levels 7.8-8.0. My cl is averaging between 6-11. I've been keeping the cl on the lower end since last year it smelled like bleach. It's a continues circle. How can I keep my cl good and my ph normal? My cya is 80. I've already added 2qts of MA since this started happening.

[swimdaddy]

A few questions:

1. What are you using to test your pool? Test strips, pool store, taylor kit?

2. What does your pH normally sit at, what is it "rising" from?

3. If using a Taylor or similar test kit, what are your other numbers? FC, CC, Alk?

Pools using chlorine will generally not smell bleachy unless the pool is dirty or fighting something, or immediately after removing the cover. My pool has almost no chlorine smell, except after a day of lots of kids in the pool (there is no "P" on my ool). After I shock it the smell goes away.

[cdingess]

Hi thanks for responding. I'm using Taylor test kit. So far this year the pool don't smell bleachy. My numbers are ph 8.0 cl 6 alk 140. My ph is rising it seems whenever I add bleach. I'll add MA the cl within a couple days will drop then I'll need to add bleach then my ph is back up. It's a circle. What can I do to keep my ph stable when adding bleach?

[cdingess]

The pool looks great just worried about ph being 8.0.

[swimdaddy]

Do you add anything else to the pool? How do you add chlorine? pH tends to go up with alk, so if your alk is high, your pH will want to be high. You could try dropping your alkalinity, some people get it down to 50-80 ppm.

[cdingess]

I haven't added anything else. I just add cl to the skimmer/pump and let it circulate. How do I decrease the alk? Do they make a ph stabilizer? Usually I use the bbb method but I don't know if this fits in the bbb method. Thanks.

[polyvue]

Hi cdingess,

How are you testing pH? With Taylor's phenol red drop test?

The CYA 80 ppm is a bit high, forcing you to maintain your pool with fairly high chlorine levels. Enough to produce a false high pH reading when using phenol tests.

It would seem like the pH is rising whenever you add bleach but it's probably just that the chlorine has affected the pH test. You could test this proposition by waiting to test pH when total chlorine falls below 5 or 6 ppm. Or borrow someone's pH meter to verify.

Or you could dilute your high-chlorine sample water sufficiently (with distilled water) to get a correct pH reading.

I think Taylor warns about interference with the pH test at chlorine levels above 10 ppm but my own testing leads me to believe the dark purplish color that affects the test starts at lower levels (maybe 8 ppm FC?)


"Do they make a ph stabilizer?"

Yep. Except you're already using it... :) Sodium Bicarbonate is a buffer, as is Sodium Tetraborate. I'm not sure TA 140 is high enough that I would want to lower it through the recommended 'Lower the pH and aerate' routine. It's a hassle and takes forever (a few days).

OTOH if your makeup water has much lower TA, it may be worth the time & effort to dump some pool water. This would lower your CYA, too.

Lastly, I assume when you say "bleach" that you mean sodium hypochlorite (liquid chlorine 5 to 12%) from the grocery or pool/hardware store. If you're adding other compounds, they could contribute to higher pH (not trichlor, which would just escalate your already high CYA).

[FormerBromineUser]

Here is how you lower TA: http://www.poolsolutions.com/gd/lowering-swimming-pool-alkalinity-step-by-step.html

[JimK]

Hi cdingess,

How are you testing pH? With Taylor's phenol red drop test?

The CYA 80 ppm is a bit high, forcing you to maintain your pool with fairly high chlorine levels. Enough to produce a false high pH reading when using phenol tests.

It would seem like the pH is rising whenever you add bleach but it's probably just that the chlorine has affected the pH test. You could test this proposition by waiting to test pH when total chlorine falls below 5 or 6 ppm. Or borrow someone's pH meter to verify.

Or you could dilute your high-chlorine sample water sufficiently (with distilled water) to get a correct pH reading.

I think Taylor warns about interference with the pH test at chlorine levels above 10 ppm but my own testing leads me to believe the dark purplish color that affects the test starts at lower levels (maybe 8 ppm FC?)


"Do they make a ph stabilizer?"

Yep. Except you're already using it... :) Sodium Bicarbonate is a buffer, as is Sodium Tetraborate. I'm not sure TA 140 is high enough that I would want to lower it through the recommended 'Lower the pH and aerate' routine. It's a hassle and takes forever (a few days).

OTOH if your makeup water has much lower TA, it may be worth the time & effort to dump some pool water. This would lower your CYA, too.

Lastly, I assume when you say "bleach" that you mean sodium hypochlorite (liquid chlorine 5 to 12%) from the grocery or pool/hardware store. If you're adding other compounds, they could contribute to higher pH (not trichlor, which would just escalate your already high CYA).

My experience with the Taylor pH test kit has been the opposite from yours. As long as I take a reading immediately, I've gotten accurate readings with FC as high as the mid teens. The key being to take the reading immediately. :)

[polyvue]

Interesting. I would estimate that for me the time elapsed between sample collection and the pH test is usually under 5 minutes. I almost always conduct a FAS-DPD chlorine drop test first, using a 'speed-stir'. Even with a color corrected daylight lamp, when the chlorine is high ( 7-8 ppm+ ) visually matching the pH of the treated sample to the color standards is challenging.

At the very high levels of FC that you're reporting --15 ppm?-- the sample appears to greatly exceed the highest standard (8.2 using midget comparator) and is dramatically purple. Yet dilution of the sample with deionized water seems to correct for this... my pool water typically varies from 7.4 to 7.8 pH in the summer.

Taylor recognizes this as a potential interference for the test in K-2006C kits but doesn't mention dilution of the sample. Just tells the user to 'wait'... :puzzle:


Sanitizer levels > approx. 10 ppm may cause a blue-purple color resulting in false high readings. Wait for sanitizer level to decrease to normal levels and retest to assure an accurate reading.

http://taylortechnologies.com/products_PotenInterf.asp?KitID=2235


Nothing about pool chemistry surprises me anymore. The remaining mysteries are intriguing.

[JimK]

Sorry, I wasn't clear. When I say to take a reading immediately, I mean immediately after adding and mixing the pH reagent with the water sample. If I let it sit after adding the reagent, it will change to purple /false high; the higher the FC level, the faster the color change to false high occurs.

I've certainly never had a problem with the pH test at FC levels below 10 and am surprised you're having trouble unless you're adding the pH reagent and letting it sit.

[polyvue]

Sorry, I wasn't clear. When I say to take a reading immediately, I mean immediately after adding and mixing the pH reagent with the water sample. If I let it sit after adding the reagent, it will change to purple /false high; the higher the FC level, the faster the color change to false high occurs.

I've certainly never had a problem with the pH test at FC levels below 10 and am surprised you're having trouble unless you're adding the pH reagent and letting it sit.

Wow. I see what you mean.

I had noticed in the past that in a treated sample the apparent pH would change during the first few seconds of observation (at higher levels of chlorine) but hadn't fully appreciated the rapidity since I would routinely discard the result ("not tested") or retest using a dilute mix.

I performed a test this morning to explicitly compare the two approaches: '1 - Immediate Reading' and '2 - Dilute Sample Before Testing'. A quart of sample water supplied both tests. FC 6.8 ppm before and after, from original sample cup.

For the 'Dilute Sample' test, I decanted 1/2 C. sample water into a rinsed 2-Cup glass measure, then added 1/2 C. distilled water, swirling to mix. Thereafter, this was used in the same manner as the sample water for the 'Immediate Read' test, first used to rinse the test cell and then fill it to the calibration mark. In each test, a .5 mL pipet of Taylor R-1003J pH indicator solution (Phenol Red) was added to 11.5 mL sample in the test cell, capped and upended quickly to mix. Immediately, the sample color was compared to the liquid standards and recorded.

I was dumbstruck with how fast the sample in the first test changed color... in little more than a couple of seconds after noting the initial color it was already changing, and was out of range before I could count past three (seconds). In contrast, the Dilute Sample test was uneventful. I don't have an arbitrator to conclude that my testing method or result is correct. Time to get a pH meter?

Immediate Reading

~ 1 second - 7.7 (intermediate between 7.6 and 7.8, light purple)

~ 3 seconds - 8.2+ (clearly exceeded test range, deep purple)

~ 1 minute - 8.2+ (no change, remained deep purple)

Dilute Sample

~ 1 second - 7.5 (intermediate between 7.4 and 7.6)

~ 3 seconds - 7.5 (no change, remained pinkish orange)

~ 1 minute - 7.5 (no change, remained pinkish orange)

The sample water used for the pH test was only FC 6.8 ppm CC < .2 ppm (34 drops FAS-DPD titration reagent, 25 mL sample, tested before pH tests and a minute or so afterward). I didn't think to test FC on the dilute sample before discarding! Other parameters: 85 degrees F., 10 ppm borates (est.), 720 ppm salt, 250 CH, 125 TA, 35 CYA

Are chemgeek or waterbear still contributing here?

My sincere apologies to the OP for taking over your thread.

[JimK]

Interesting. I noticed the reagent you're using is different from the one I'm using, Taylor R-0014. Perhaps this explains the difference in our experiences?

Under 10ppm FC, I can take my time reading the result. It doesn't change near as fast as it did for you until my FC gets above 15ppm FC or so.

It would be great if Chemgeek would pop in and give his input. :)

To the OP - my apologies also for the sidetrack, though it may relate to what you are seeing. How long to you let the pool circulate after adding chlorine before you check pH? What's the FC level at the time you check pH? As you can see by our discussion elevated FC can give a false high pH reading.