Borate application, redux

[chem geek]

Point 1: See the Are Borates Safe? thread for more details. The EPA limit for Borates is around 50 ppm due to the dog studies, a margin of error (MOE) of 100 and presumed small amounts of ingested pool water. It's all very conservative, but maximum label dosings would be no more than 50 ppm these days.

Point 2: The following table shows the equilibrium carbonate alkalinity vs. pH where the amount of carbon dioxide in the water is in equilibrium with that in air.

pH CarbAlk
--- ----------
7.0 ..... 3
7.1 ..... 4
7.2 ..... 5
7.3 ..... 6
7.4 ..... 7
7.5 ..... 9
7.6 ... 11
7.7 ... 14
7.8 ... 18
7.9 ... 23
8.0 ... 29
8.1 ... 37
8.2 ... 46
8.3 ... 59
8.4 ... 76
8.5 ... 98
8.6 . 127
8.7 . 165
8.8 . 216

However, the rate of carbon dioxide outgassing varies as the square of the CarbAlk so in practice the lower TA significantly reduces the rate of pH rise and does not need to be as low as the above equilibrium values. As waterbear noted, in practice a TA of 50 ppm is usually pretty stable in spas if 50 ppm Borates are also used (and along with 30 ppm CYA the CarbAlk will be around 30 with the pH at 7.7 to 7.8). However, if you've got heavy use of aeration jets in a spa, then an even lower TA may be needed.

Point 3: I disagree with waterbear on this one. I wouldn't say that there is any tendency of the borate buffer system to move the pH at all. It is the carbonate buffer system that moves the pH upward based on the out-of-equilibrium situation described in Point 2 above due to carbon dioxide outgassing. What waterbear is referring to in terms of up and down are the pH positions of maximum buffer strength (aka buffer capacity though it isn't really a capacity) which for the carbonic acid (really mostly aqueous carbon dioxide) / bicarbonate buffer system is at a pH of 6.3 while for the borate buffer system is at a pH of 9.15. So the carbonate buffer system gets stronger as the pH gets lower so it is great at preventing the pH from getting too low, at least until the TA is near exhausted. Likewise, the borate buffer system gets stronger as the pH gets higher so it is great at preventing the pH from getting too high.

[waterbear]

Point 3: I disagree with waterbear on this one. I wouldn't say that there is any tendency of the borate buffer system to move the pH at all. It is the carbonate buffer system that moves the pH upward based on the out-of-equilibrium situation described in Point 2 above due to carbon dioxide outgassing. What waterbear is referring to in terms of up and down are the pH positions of maximum buffer strength (aka buffer capacity though it isn't really a capacity) which for the carbonic acid (really mostly aqueous carbon dioxide) / bicarbonate buffer system is at a pH of 6.3 while for the borate buffer system is at a pH of 9.15. So the carbonate buffer system gets stronger as the pH gets lower so it is great at preventing the pH from getting too low, at least until the TA is near exhausted. Likewise, the borate buffer system gets stronger as the pH gets higher so it is great at preventing the pH from getting too high.

Actually, we are saying the same thing if you think about it. My wording was trying to put in more layman's terms what occurs. It is easier for most to understand 'moving the pH" since that is what they do with the addition of an acid or base and it is easy for them to think of a buffer as something that does that for them automatically.

[waterbear]

Point 1: See the Are Borates Safe? thread for more details. The EPA limit for Borates is around 50 ppm due to the dog studies, a margin of error (MOE) of 100 and presumed small amounts of ingested pool water. It's all very conservative, but maximum label dosings would be no more than 50 ppm these days.

As a point of interest Bioguard recommends 30 to 50 ppm of Optimizer for halogen sanitized pools and 50-80 ppm for biguanide santized pools (probably for the algaestatic action of borate).
Then again, we used to use simazine as an algaecide in pools until it was banned. I am sure Ben is familiar with it.

[chem geek]

In my post above "margin of error (MOE)" should be "margin of exposure (MOE)". It's too bad that I can't edit my posts after some time.

Yes, as shown in the Bioguard® Optimizer Plus® instructions, they recommend 50-80 ppm for biguanide pools. This is somewhat higher than the 50 ppm limit implied by Table 5 of the EPA report that has a 100 MOE for a roughly 350 mg/L sodium tetraborate pentahydrate product concentration which is equivalent to 350 * (4*10.8117/291.3) = 52 mg/L (ppm) Boron. I suspect that the biguanide dose rate is grandfathered.

As for the buffer explanation, I think it would be better to refer to the buffer as resisting moves in pH rather than moving the pH itself (at least for the buffer part of the explanation -- carbonates have a separate carbon dioxide outgassing effect that is not related to their buffering). The borates resist moves of pH in both directions, not just down, but since the resistance gets stronger as the pH rises it acts like a spring being compressed at higher pH just as the carbonate buffer acts as a spring being compressed at lower pH. So the carbonates resist the pH getting too low while the borates resist the pH getting too high even though technically they both resist pH changes in both directions at any given pH. A key point, however, is that the carbonates (represented by TA) are a SOURCE of rising pH in their own right, due to carbon dioxide outgassing, and that has nothing to do with their buffering capability -- it is an additional and unique effect that does not apply to borates. So substituting borates for carbonates as a buffer system makes sense to reduce a source of rising pH.

[waterbear]

I like that spirng analogy! Mind if I use it in the future?

[chem geek]

But of course...use it freely! The most important point, though, is that the carbonates are a SOURCE of rising pH in their own right. So while they buffer pH, they also CAUSE rising pH. That's the most critical concept to understand. Otherwise, if we only talk about buffers and how they get stronger in one direction or another, then people will think that they can balance each other out and that having a higher TA is no problem if you just have more borates. That isn't true, of course, though the borates may make the rate of the pH rise less, there will still be as much acid that needs to be added. The only real way to save on the amount of acid needed is to lower the TA (and/or have a higher pH target -- i.e. don't try and lower the pH as much).

The thing I don't like about the spring analogy is that it still implies some sort of pressure or movement when it's more like resistance to change. That is, though the spring will make it harder to compress, it isn't really causing the pH to bounce back the other direction after you stop adding acid or base. It's more like viscosity where it gets more viscous so harder to move as you get closer to the pH buffer's strongest pH point, but once you stop applying acid or base, it stops moving (except for the carbon dioxide effect which is essentially removing carbonic acid from the pool).

[PoolDoc]

I've tried to write a full response 4x now but I keep getting side-tracked. Sorry!

I'm going to try again, but rather than writing a response, I'm going to try to summarize the issues and state my view. If you disagree, and can prove me wrong, or justify an alternative position or conclusion, I would be grateful of you do so. I don't like being proved wrong, all that much, but I like it much better than BEING wrong!

Probably, each point could be its own thread; feel free to spin off a thread if that will avoid confusion.

OK. Issues.



0. (This is not really a conclusion; just a bit of information.) At PF, for every person who registers, there are more than 25 who just lurk! That's good! We could not answer 25x as many questions as we do.

So, some of my positions here, reflect the sense I always have of 25 lurkers with pools, who are reading over my shoulder.

1. At PF, I prefer the least accuracy and simplest explanation consistent with both truth and function. Chem_Geek and I have talked about this before: he prefers more accuracy. I have not always thought this way, to the degree I do now. But even when I was working on the testkits, my ORIGINAL goal was mostly to get pool owners out of pool stores, and I felt I needed a more accurate kit, in order to get pool owners to trust their results.

2. I do NOT want posts at PF that suggest that pool owners measure 32% muriatic acid, beyond 1/8th or 1/2 of a gallon jug. I've opened a thread on this in the Contributors' section. If you disagree, I welcome your input, but please take it there.

3. I decided a long time ago to prefer the "dose, test, dose, test . . ." (DT) approach to pool chemistry over the "test accurately, calculate, measure carefully, dose" (TCMD) approach that pool stores claim to use. The ONE exception to this is chlorine dosing, where pool owners often need enough (or a little more) RIGHT now.

One reason (among many) for my preference is that the TCMD approach can only work consistently if the TEST are accurate AND the CALCULATION is accurate AND the MEASURING is accurate AND the pool volume numer is accurate. In my experience, it's rare that all these coincide.

4. Given the 3 points above, and given my very considerable skepticism about Girvan's 'studies', I can't see any benefit to the elaborate 'official' program pushed by Proteam. Maybe there is one, but you'll have to explain it do me. I don't doubt that it works; I just don't have any reason to think it works better than a simple DT approach.

5. I don't like spas, and haven't for a long time. Basically, I think you can divide spas into 3 groups:
+ Spas with full-time trained attendants or with functioning ORP/pH controllers, calibrated daily, that trigger reliable bleach and acid feed pumps;
+ Spas attached to pools, that SHARE water and treatment with the pool; and
+ Heated cesspools. (I think this is by far the largest group!)

I'm open to the possibility that a spa with an attached high-output ozone feeder could represent a 3rd group of spas that ARE sanitary. Under those circumstances the LACK of a sanitizing residual would be good, since you wouldn't have to deal with the ozone equivalent of the spa with 200ppm Br. (Been there; somebody else did it; did see the saggy bathing suits!)

6. We have enough PF users with IG pools and attached spas, so that I've got to get over myself, and create space for spa answers that are good, or at least, as good as they can be. (I still don't see any way that, given how people are, there's anyway for non-automated, non-attended stand-alone spas to be anything but cesspools . . . or chemical fire-pits!

7. There is no way to maintain carbonate alkalinity in a spa IF pH levels are maintained in the 7.0 - 7.8 range. I discovered that 20+ years ago, after installing a bleach / acid feed system, and an ORP/pH controller on the Marriott in Atlanta. I balanced everything just so; turned on the feed system, adjusted it; turned on the controller and calibrated it . . . and then turned on the blower. 10 minutes later, my 120 ppm TA was below detection with the Lovibond tablets I was using then. Rebalance; repeat; same result. Do over, again. Fortunately, I had my Eureka! moment, before going for a 4th time.

8. Pools with attached spas, are pools with super-high-output aeration. If the spa is used regularly, CA cannot be maintained on those pools, either.

(I made a BIG mistake in my answer in the thread that triggered this: I assumed that, since the OP said his pH rise was related to his SWCG, it was. But, based on the info we have from him, it's just as likely it was from his spa aeration.)

9. If we're going to deal with spas, we need to make SURE we know which type the OP is talking about: (a) stand-alone, (b) shared equipment, but NOT shared water, (c) integrated. In most cases, only integrated spas can be consistently sanitary. And, we need to make sure that WE have made clear which type it is, so the lurkers will understand.

10. I need to write a "using borax" page that includes borax hazard info. Then, we need to reference that page in borax posts, partly as CYA, and partly so people who are frightened of chemical hazards will be able to trust us.

11. I think Chem_Geek settled it, but I'll state it: buffers cause water to resist pH change; they do not cause or push pH change themselves. In water systems that already have a drift, due to SWCG use, aeration, or trichlor use, different buffers will great different 'stop' points in the pH drift. Buffers (that I know about) in pools include carbonates, cyanurates, phosphates and borates. I don't think phosphates are deliberately used anymore, with the demise of "Perfect pH".

(I like the viscosity analogy much better; an alternate might be driving on concrete vs driving in loose sand, or something along that line. It might be possible to apply the spring analogy to the way CA 'disappears' when the pH drops, but 'reappears' when it goes up. But, that just popped into my head; I haven't considered it.)

12. . . . that's all I can think of, now.

[Gotta go -- will check for spelling & other errors when I get back]

[chem geek]

There are plenty of spa owners at poolspaforum.com who use the Dichlor-then-bleach method (Dichlor used initially for about a week to build up CYA and then switch to bleach) and are able to keep their pH and TA fairly stable by having the TA be low (usually 50 ppm or a little lower), using 50 ppm Borates, and not trying to keep the pH much below 7.8 though some find the pH to be OK in the 7.5 to 7.7 range. Now keep in mind that these are residential spas so typically not used more than once a day. The water stays in good shape for about twice as long as Dichlor-only users (probably due to CYA build up making chlorine less effective). I would not characterize them as cesspools though it is true that they build up some organics that are not fully oxidized but the only indicator of that is a slowly increasing chlorine demand from around 25% per day to 50% per day. Ozonators are a mixed bag, but for high-use spas they help while for low-use spas they mostly just increase chlorine demand.