PH and Sodium Hypochlorite

[gregsfc]

What's going on with the chemistry when maintaining fc above, say 6 with regards to a red-drop ph test when using sodium hypochlorite as the source of chlorine? I know that you guys say don't test for ph above 10 or so in order to get an accurate ph reading, but my experience tells me that anything above five will always give me a higher ph result than what I'll get if I let fc drop down below 6 before testing ph. Is it simply that the test is invalid and not indicating anything real at higher fc levels and ph is really not affected, or is it more correct that the ph temporarily increases when there is higher concentations of sodium hypochlorite in pool water? I'm just trying to understand what's going on chemically when a test is conducted at high fc levels, and also, does this apply only when sodium hypochlorite is the source of chlorine used?

Thank y'all for what you do. I recently renewed my bronze status, because finding this site and this method of pool care and using it now, going on four years has saved me so much time, energy, and money. Thirty bucks is a great deal in return for what y'all have given me in pool care knowledge amd tools and personal advice.

 

[Donldson]

Are you using a Taylor pH test? Their pH reagents are formulated to be reliable up to 10 ppm FC, but other kits tend to top out around 5 FC and some even as low as 3 FC.

 

[gregsfc]

I've got a TF-100, but my OTO/PH tester is Clorox. I guess where I didn't replace the OTO/PH when I ran out of reagent. Maybe I need to get a Taylor replacement. Usually isn't a problem, but this year I over shot my CYA target and am managing at 60 for a non saltwater pool meaning I'm almost always above 5 and have to let my FC drop to the absolute minimum to get a good PH test result. PH stays rock steady, but I still like to check it out every week or so. So you're saying it's just an invalid test result and the PH isn't actually rising with higher FC levels right?

 

[cfherrman]

Use the k1000 that comes with the tf100

 

[gregsfc]

Use the k1000 that comes with the tf100

I would if I still had it. I got the TF100 years ago, but have just been replacing reagent about every year and a half (the reagents that I actually use). At some point, I misplaced that K1000, as you call it, still had the reagent bottles but lost the rest of the kit. I bought that Clorox kit, but couldn't confirm if the tubes in that kit had the same volumes as that K1000, and so I've been using those reagent for a little more than a year. The Taylor reagents that came with the Taylor kit are now too old. That's an easy fix. I'll get the Taylor kit, and that will help me better manage PH at higher FC levels. I didn't realize the OTO/PH reagents were different. That's very helpful.

Back to chemistry...Do these recommendations about using a different kit mean that sodium hypochlorite is PH neutral and my lower FC testing is the correct PH level in my pool? I'm dealing with a bit of mustard algae. Wanting to make sure I'm not helping the algae by keeping PH higher than it needs to be if it's actually higher during times when the FC is higher. I've had the mustard algae about a year, but didn't realize it until recently. On my way towards learning that the poof-away sand-looking stuff in the middle of my pool is actually mustard algae, I raised my PH from 7.1 to 7.3 after I let my FC drop to 5, which I did to get a good PH test result. My PH had dropped slightly below the minimum range after my CYA add at the first of the season. I did the PH adjustment only after I realized that it was not going to recover on its own as it sometimes does after a CYA addition. After that very slight PH adjustment via just a bit of borax, I started getting some yellowing on my vinyl floor that was not occurring before that time, as if the mustard algae took a little better hold after the PH was brought up by .2. Once that yellowing showed up, I couldn't seem to get it brushed off. I just completed mustard SLAM, went right to the mustard algae shock level for CYA at 60 after one night at regular shock level, because I was already passing all three criteria even before I started SLAM as advised on the SLAM forum by the wonderful TexasSplash. Now I've got to see if the mustard algae will stay gone over a period of time. I still don't have the yellowing completely gone from my floor although it is very faint and I've brushed it in all directions probably fifty times with three different brushes. My theory is that it was either letting FC drop to 5 (which should be okay with cya at 60, but maybe not with mustard algae), or the fact that I slightly raised the PH that gave the mustard algae a little boost in my pool, as I've been targeting FC at 10-10.5 prior to my recent SLAM after I confirmed that my PH is truly 7.3.

 

[ajw22]

pH of 7.1 is as good as 7.3. Any pH in the 7s is ok. Stop micro managing your pH.

PH - Further Reading

www.troublefreepool.com

What is the Effect of Adding Liquid Chlorine on pH?
It is a myth that liquid chlorine will raise pH. The myth is based on a misunderstanding of chlorine chemistry.

Adding liquid chlorine to water can cause a temporary increase in pH which is usually offset by the chlorine reacting with organics and biological matter which are acidic (creates a proton) reactions. Thus, on balance, the net chlorine reactions are pH neutral.

Most retail and commercial liquid chlorine products contain a small excess of lye from the manufacturing process but this amount of OH- is minimal and does not change the pH with normal levels of liquid chlorine use.

If one were to add significant amounts of liquid chlorine (for example, raising the pool water chlorine concentration to SLAM FC levels), then the pH rise would need to be offset by an initial lower of the pH with acid. This is why TFP requires a pool owner to adjust their pH down to 7.2 prior to starting the SLAM Process.

Adding liquid chlorine DOES increase the pH at first, however as it's used up the acid that's created lowers it back down to where it was before......thus equaling each other out making it pH neutral.

 

[gregsfc]

TFPC comes through again! That's what I'm looking for; a chemistry answer. Even though I have a hard time understanding the full chemistry explanation of things, I still get enough understanding to help out my feeble mind.

I guess I started worrying about this for two reasons:

Firstly, I over shot my cya this Spring. I will be more careful in the future. I did not carefully measure out my stabilizer this year (won't happen again), and so I inadvertently raised cya to 60 which I don't like managing FC at this high level, because I have to keep it higher, which has been making it harder to get an accurate PH test. I've been having to let the FC drop to down around the minimum for my cya level to get a good measurement, and I didn't like that, which is compounded by reason two explained below. I could tell that there is no lasting effect on PH from sodium hypochlorite, because, whenever, I'd get my FC down to where I could get an accurate PH result, it was always the same reading. For about six seeks, I had let it sit right about 7.1; just barely below that reddish 7.2 color. The PH went down just a tick after that same overshot dose of CYA. It is not uncommon that I'll drop out of PH range slightly after adding cya, but most-times, it's temporary, and it will recover. I always give it a chance to recover as long as it's just slightly below range. I was giving my PH a chance to recover, but finally adjusted from 7.1-7.3 with borax (TA has been at 50 for three years and I rarely have to mess with PH except for a couple times related to adding stabilizer). Anyway, I hit my PH target exactly, but right about that same time, I started having more issues with my 2nd worry. The other problem listed below seemed to gain steam right after the slight PH addition to put me at the low end of range. I wanted to make sure that it wasn't a mistake to move PH from 7.1-7.3 with the fact that I've been targeting around 8 on FC, and very recently about 10.5. I've ordered a Taylor PH kit, so maybe that will help with the management better since some on here say I can get an accurate measurement up to an FC of 10 using the Taylor kit. Another reason I don't like CYA way up at 60, is at the odd chance that I have to SLAM. It'll be harder and more expensive to manage shock-level FC with CYA at 60, which is what had to happen recently.

The second reason I wanted to know the chemistry about how sodium hypochlorite's affect PH level is that three weeks ago, I slowly came to the realization that I've had a mustard algae outbreak (hopefully gone for good now following Mustard SLAM procedures), I have had it for some time. I had it visibly on the floor for a while last year, and have had the loose grit this whole time, but thought that it was pollen, but when the floor started yellowing again this year (right after I put PH back in range), and that gritty stuff kept coming back, I began researching about this gritty stuff on the bottom that I can vacuum out to waste only to have the same amount showing up three days later. Anyway, I was worried more about letting the FC drop to 5 once I came to this realization, and knew that TFPC teaches that PH tests are valid up to an FC of 10, and that was not my experience, so that's why I asked the question and was pondering that, if PH is actually higher during the entire target period instead of just an invalid test, then I was worried that there was a third reason for keeping CYA below 50. The possibility that running a higher FC level was actually resulting in having a higher average PH level. Anyway, I'll be glad when I get back down to around 40 or below on CYA. Thanks again.

 

[gregsfc]

One other question: Is keeping PH in the range that the TFPC recommends considered micro managing PH? That's a very confusing statement to an average student of TFPC. I've made three PH adjustments in two years; and two of those was a couple of rounds around the same time where I ended up having to bring up TA by 5, but I have always been striving to keep PH in range and have in the past been told to do so. But it hasn't been much of a strife since I've got my TA set right, and didn't realize that I wasn't supposed to strive to keep it in range until just today.

I went through this same ordeal with TA a few years back. I kept putting PH back in range each time it would drift and reach 8.0. Over and over with muriatic acid; the TA recommendation back then was 60-100 for my type pool. I had posted here, and no one then said not to micro manage PH. After a couple weeks, of MA adjustments every two to three days, I'd test and my TA and it would be down to 50. I'd raise my TA back to mid range, because that's what the chart says and what the pool school says and I'm not chemistry minded. Someone then made an off hand comment on the thread where I'd asked for help to stop adjusting my TA, but not being a chemistry minded person, such a comment served only to confuse me, because it's basically saying that the recommended level is not right? Anyway, Mr. Falk helped me understand back then; gave me my minimum TA I could have based on CSI or something like that, and the new chart nowadays for my type pool for TA is now 50-90. Most of us think that the recommendations are supposed to be strived for, and so when we read a comment that tells us we shouldn't try to keep any specific level in a published range, that only confuses us.