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chem geek

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  1. If you have just been adding more bromine to your spa, then you haven't been shocking it at all (just as you surmised). However, something called "superoxy" is likely to be more than just bromine -- it is probably either chlorine or a non-chlorine shock (oxidizer). Perhaps waterbear knows for sure or you can look at the label and let us know the ingredients. MPS is Potassium Monopersulfate which is the most common type of non-chlorine shock. It sometimes goes by the trade name of Oxone, but is sold under many different brands. It is essentially just an oxidizer, just like chlorine and bromine, but is strong like chlorine so can be used to regenerate bromine. In a bromine spa, the bromine is essentially in two forms. The active and disinfecting form is hypobromous acid (HOBr). When this gets used up by disinfecting a pathogen or oxidizing an organic (or ammonia), it gets converted to the other form which is bromide ion (Br-). This is very similar to how chlorine works, but the neat trick here is that the bromide ion can be regenerated back into hypobromous acid by adding a stronger oxidizer to your spa, such as chlorine or MPS in a process known as shocking. If you have chlorine shock left over, you can still use it to regenerate bromine (i.e. to shock your spa). Let us know what kind of chlorine shock you have -- does it say "dichlor" in the ingredients? As for "what is superoxidizing with bromine", I don't know. It certainly sounds confusing. Maybe they meant that it "superoxidizes bromine" meaning it regenerates bromine by oxidizing bromide ion. Again, look at the ingredient label to see if it says either hypochlorous acid (or sodium hypochlorite or something with chlorine in it including Dichlor) or potassium monopersulfate (or something with "per" in it like perborate or peroxide). It sounds like the pH rise has slowed down a bit and that is good. Perhaps we are on the right track after all. Once we get things sorted out a bit, we might consider adding borates (Borax) to your spa to act as another pH buffer so at least you won't need to add acid as frequently, but right now let's take one step at a time and figure out what this SuperOxy is.
  2. waterbear was right. I was thinking chlorine, not bromine. Sorry for the confusion. The principle of lower TA causing less pH rise still applies to a bromine pool, but if the bromine source is acidic, then your pH risks swinging more wildly. Since this particular hot tub is finding strong pH rise and not pH drop, the source of disinfectant must not be that acidic so lowering the TA is appropriate. The fact that the TA dropped so readily at lower pH (and with aeration) does seem to indicate that we may be on the right track here. Let's see if it works in this situation...I'm holding my breath and keeping my fingers crossed waiting for the final result...
  3. Well, with how you answered the questions, I'm not as certain that the spa being overcarbonated is the cause. If you measured the pH AFTER your 45 minute session and put on the cover and then measured the pH just BEFORE your next 45 minute session and saw the pH rise, then that would tend to invalidate what we think is going on. However, you probably measured the pH at two points in time straddling one or more 45 minute sessions, and if that is so then the total of 90 minutes of strong aeration with high TA per day could certainly lead to a strong pH rise. So, let's try what we suggested (i.e. lowering your TA) since if it doesn't work it's trivial to increase your TA back up (though still probably not to 130). As for "too high" in TA, the recommendation of 120-150 ppm is, no question about it, too high. Somebody probably thought that with such a small water volume in a spa that extra pH buffering would be a good thing, but they forgot that the pH buffering using sodium bicarbonate also has the side effect of wanting to increase pH. And yes, technically, your TA is too high for your conditions. Someone with a pool that has a cover on it (like I do, with an electric cover) and no aeration to speak of (no waterfalls, upward jets, or water features) could probably live with 120 ppm TA. This would be especially true if an acidic source of chlorine, such as Trichlor tablets, were used. However, with a somewhat neutral chlorine source and without a pool cover, even a pool shouldn't have much more than 100 ppm TA and 80 ppm TA is better. In situations where there is aeration, such as with a waterfall (or an SWG that generates hydrogen bubbles), even lower TA, but generally above 50 ppm TA, helps keep pH more stable. This concept of lower TA actually stabilizing pH is one of the hardest and most counterintuitive things I have encountered in pool water chemistry. Even though I understand the chemistry of what is going on, it is still quite strange. I guess the best way to understand it is to think of higher TA doing two separate things. On the one hand, higher TA buffers the pH so that for a given amount of acid or base that is added, the pH moves less at higher TA than at lower TA. On the other hand, a higher TA represents more bicarbonate in the pool including dissolved carbon dioxide and this amount is quite a bit higher than found in air so it outgasses. When this happens, it makes the pH rise. Technically, HCO3(-) + H+ --> H2CO3 --> H2O + CO2(g) so you can see that a hydrogen ion gets removed from the water as carbon dioxide is outgassed. pH is just a measure of hydrogen ion in the water with lower pH having more hydrogen ion so with less hydrogen ion the pH goes up (the opposite direction is due to the fact that pH measures the NEGATIVE of the logarithm of concentration which was probably defined that way so that the pH numbers would normally be positive in value). I'm not going to try and fully explain why the TA doesn't change since that is even more complicated, but is essentially based on the fact that each species in the first part of the equation affects TA in opposite directions so they cancel out (just as their charges cancel out). It turns out that the pressure of high TA on increasing pH outweighs its extra buffering capability so that IF the primary source of pH change is from the carbon dioxide outgassing, then lowering the TA will lower this pH rise effect by more than the reduced buffering at lower TA. So the net result is that lower TA has less of a pH rise. Clear as mud? Let's just try it out and see what happens. We're all practical people and whatever works is what is most important. I'm just a geek and like to understand what's going on more technically in the hope that I might find some solutions that I otherwise wouldn't have if I didn't possess the extra knowledge.
  4. There aren't any signficant issues with using bleach for shocking, per se. But if you don't use ANY dichlor and have no CYA in your tub at all, then your effective active chlorine levels will be much higher. That's good for killing bacteria that causes hot tub itch, but it will also wear on your swimsuits more and you may notice more chlorine smell. If these become issues for you, then using a small amount of dichlor -- about 5 ppm FC worth -- would cut down the active chlorine some, but not too much. You might think that without CYA you could just keep your FC down really low, but you need enough FC to be in reserve as it gets used up especially while you are in the tub (sweating which contains urea, for example). So having some CYA will let you keep your FC up for the reserve but not having too much CYA will keep the active chlorine effectiveness up. A dicey balance, but I'm much more "geekily" concerned about this than you need to be. So if I were you I would try out the bleach-only for a while and see if there are side effects for you. If there are, then use a little dichlor. That sounds like a decent compromise. waterbear can probably tell you a lot more since he has a spa as part of his pool with a spillover (or do I have your pool/spa mixed up with someone else?). He uses an SWG now, but I believe used bleach before the SWG was installed. By the way, waterbear, it looks like we've got another chemical mystery on our hands that needs to be sorted out. Namely, the use of dichlor but with no CYA getting measured. I suspect you are quite right that the higher temperature dissolves more precipitate so that would make the CYA test quite temperature dependent indeed! Gee, it would have been nice for Taylor to mention that. I think I'll send them an E-mail -- they always like hearing from me! (actually, they do). [EDIT] It looks like mealmine cyanurate (which is the precipitate) is soluble in water at 0.002g/100ml at 20C (68F) which works out to 20 mg/l or 20 ppm. So if this is correct, you don't even START to see cloudiness until 20 ppm (so how does my K-1720 test kit measure down to 20 ppm?) so that's another question to ask Taylor.
  5. waterbear, thanks for the caution on Muriatic Acid. I forgot that the tub is small and would require very careful small measurements of acid addition. One thing that bothers me a little bit with this situation is that there was no TA drop seen during the pH rise, acid addition cycle. The drop would be quite small but over time should have been noticeable. So it is possible that there is some other source of pH rise so I have another questions: What is your new spa made of? Is it plastic or is this some sort of in-ground plaster/gunite spa? If the latter, then at least some of the pH rise is likely from the curing of the plaster/gunite (concrete). Or does your spa have new tile in it with grout? That would also cure and the curing of concrete causes a significant rise in pH as it absorbs water and releases calcium hydroxide. Anyway, it's just another thought.
  6. A few questions: 1) Do you keep a cover on your hot tub when not in use and how long is it uncovered during the time that the pH rises? 2) Do you keep the jets on or have other aeration during the time you see the pH rise? You said the pH rose when it wasn't in use, but wasn't sure if that meant the jets were off during that period of time. Is your hot tub outside and was it windy when the pH rose (assuming there was no cover)? 3) What kind of sanitizer are you using? Is it bleach or Dichlor, Bromine or something else (small SWG)? The most likely cause for your rise in pH is the combination of a high TA and high aeration. TA measures Total Alkalinity and that is mostly from carbonate in the water (you probably added sodium bicarbonate or baking soda to the water initially) and that essentially makes your spa "a lovely carbonated beverage" so to speak. It has a lot more carbon dioxide dissolved in it than is found in the air so it outgasses it. When this happens, it makes the pH rise (ironically, the TA measurement stays the same, and I won't go into the technical reasons as to why this is true). IF the pH rise is due to the outgassing of carbon dioxide and not to some chemical addition to your spa, then LOWERING your TA is the answer to your problem. This is ironic because TA is normally considered to buffer pH, but it turns out that the effect of pH rise from too high a TA outweighs the lower buffering effect from a low TA. There are two ways to lower your TA. First, you could drain and refill your spa and add less baking soda to get to 70 ppm. That's the expensive approach since you need to add chemicals, but it is relatively fast. The second option is cheaper but requires some patience. It is to lower your TA in your existing water and the way you do that is to lower your pH significantly, to around 7.0 (or at least 7.2) assuming your test kit reliably measures that (i.e. that it isn't the lowest measurement on the pH scale of your test equipment) and keep adding acid to keep the pH low AND aerate your spa with all the jets on and pointed up. This will bubble out the carbon dioxide which has the pH rise and your adding acid lowers both the pH and the TA -- net effect is lowering of TA (removing carbonate from your water). When the TA measures a low value, such as 70 ppm, then stop adding acid and let the pH rise by just aerating. The pH should now settle down and be more stable in the 7.5 region or thereabouts. You might still need to add acid periodically, but probably a whole lot less. Also, you have been using sodium bisulfate as your acid and that increases sulfates in your water, which isn't horrible but you could also (carefully) use muriatic acid which would add chloride to your water. Yes, you increase your TDS either way, but chloride is very benign and would just make your spa more like a salt pool. Of course muriatic acid is a harsher chemical, mostly because it's a concentrated liquid that somewhat fumes. Since aeration is also a factor, after you get your TA low you should keep your hot tub covered when not in use and keep the jets off as well. That should significantly cut down the pH rise especially combined with the lower TA. Good luck and definitely keep us posted on your progress and if this helps. It has worked for others with pools (especially those with SWG systems) and a few with spas (on another forum).
  7. Your drinking water may be sanitized with chlorine and as the water travels through the pipes it may encounter pathogens or organic material and convert the FC into CC. It is also possible that your drinking water is being sanitized with monochloramine which would immediately register as CC (though that wouldn't explain the FC you are seeing). Either way, yes, you can simply shock after you refill in order to get rid of the CC (you may still register a small amount, perhaps 0.2, but that's OK). As for the CYA, it doesn't make any sense at all that you measure virtually no CYA if you have been using dichlor for sanitizing and have been doing so for a month. For every 1.0 ppm of FC increased by using Dichlor, you introduce 0.9 ppm of CYA. Perhaps you only used 5 or 10 ppm of FC over that month, does that sound right (it seems too small to me)? Such a small amount might not show up in the CYA test. At least the first 5 ppm of CYA might not show up cloudy at all as the first "precipitate" is actually a little soluble. [EDIT] A few additional thoughts I had. First, make sure you really shake the mixture of the CYA reagent with your spa water for 30 seconds. It won't form a percipitate unless it is mixed quite well. Second, I assume that your spa is kept covered except when you use it and that it is not exposed to sunlight when it is used. If for some reason it is exposed to sunlight, then you would need to use some CYA but as I mentioned in the earlier post, that's a bad catch-22 since you want a lot of disinfection for a hot tub (which CYA reduces). Third, there is a bacteria that will breakdown CYA, but it is anaerobic (meaning it lives in oxygen-free environments) and that is unlikely in your hot tub (it's more common in soil and in still pools in very cold water, which is probably why CYA levels sometimes drop in pools over a winter). [END-EDIT]
  8. I assume you have no CYA in your spa (i.e. don't use Trichlor tabs or Dichlor powder). If you do use Dichlor, then you need to test your CYA level, but generally you don't want to use CYA in a spa unless it's going to be uncovered in direct sunlight (during usage or at other times). [EDIT] We now know that you DO want to use Dichlor initially or add pure CYA to get to around 30 ppm CYA; otherwise the active chlorine level is too strong and too harsh on spa covers, swimsuits, skin, outgasses faster, etc.) Killing the bacteria Pseudomonas aeruginosa that causes hot tub itch requires rather high levels of active chlorine and using CYA will significantly cut down active chlorine levels. As for your combined chlorine, this is what is produced when chlorine combines with ammonia/urea and organics in your water. My guess is that your chlorine level was too low at some point given how many people were in the tub (i.e. high bather load) and got overwhelmed so combined chlorine built up. If the chlorine level is high enough, then the combined chlorine will go to breakpoint which releases nitrogen gas and produces chloride ion (i.e. salt) at which point the CC drops back down close to 0. If you had too much CYA in your tub, then it can be very hard for the chlorine to reach breakpoint quickly enough -- the creation of combined chlorines is a rather fast process (especially with ammonia/urea), but achieving breakpoint is generally much slower (about a half-hour if no CYA). So this is yet another reason not to use CYA in your hot tub (it makes achieving breakpoint that much harder). If you weren't checking your CC regularly, then at some point it started to build up and if you don't catch it early, it will continue to grow and grow (because the FC is not 10 times the CC so you build up harder-to-breakdown intermediate products instead of simple chloramine). In an outdoor pool, exposure to sunlight helps achieve breakpoint so that is how pools, even with CYA, avoid having CC rise. Also the bather load (people per volume of water) is much, much lower in a pool so the chlorine is much less likely to get overwhelmed (i.e. the FC is always > 10 times the CC). If you were able to expose your hot tub to UV from sunlight (or UV lamps), you could breakdown some of the CC, but that's probably not an option for you so... As for how to rid yourself of the CC, yes you need to add 10 times it's level in chlorine, but as you point out that's awfully high. I can't say if 70 ppm would bleach out anything in your tub. It might be easier, in your case, to just dump and refill the water which is something you should be doing every so often anyway (after a month of daily use, your water could probably use a full refresh). In the future, monitor the chlorine levels, including CC, more closely and when the CC is anything more than 0.5 ppm, shock with more chlorine. At that point, adding extra chlorine when the CC is, say, 1 ppm is not a big deal as 10 ppm isn't too high. If you still find it difficult to manage avoiding CC buildup, you can use a non-chlorine shock such as potassium monopersulfate (KMPS) which will combine with ammonia/urea and organics before chlorine and avoids CC completely. This also has the advantage of reducing disinfection by-products (DPBs) which would be greater in a spa without CYA and at higher temperatures. There is an unfortunate catch-22 with hot tubs in that, to avoid hot tub itch, they require higher levels of active chlorine than pools and that means using little or no CYA. You also need enough FC to not "run out" from the heavy bather load so that probably means at least 3 ppm and probably closer to 5 ppm FC. However, such high levels of active chlorine will definitely wear on swimsuits. My wife uses an indoor pool in the winter where, apparently, no CYA is used (it normally isn't used indoors), and her swimsuits last only one winter when using that pool -- the rubber wears out first and then the swimsuit shows signs of fading. In our own outdoor pool that uses CYA, the swimsuits never show any signs of wear. I haven't really figured out a good answer for hot tubs. Perhaps using a very, very small amount of CYA might be OK, but not more than 10 ppm. Unfortunately, the test kits only measure down to 30 ppm on most kits including the K-2006 (though the K-1720 measures down to 20 ppm).
  9. turbottt1, Your points are all valid. Using chlorine for a spa has all of the advantages as using it in a pool such as much more stable pH. To get that stability in pH, you need to keep your TA much lower than you would have in a pool and that should be fine so long as your spa is not plaster/gunite nor have tile with grout surfaces (and even so, you could STILL have the TA at around 50 without serious problems so long as you don't let your pH drift down too low). The reason is all of the aeration in the spa would outgas carbon dioxide causing the pH to rise. As for whether the chlorine is dangerous to your spa cover or other materials, the answer is generally no. The concentration of chlorine in the air when it is in equilibrium with the chlorine in your spa (with the cover on it) is on the order of no more than [EDIT] 100 parts-per-trillion (yes, that's trillion, not million, partial pressure) [END-EDIT] if you don't use any CYA (which you generally shouldn't for a spa unless it's in direct sunlight in which case you have a dilemma). That's a very weak concentration of chlorine so should not do much damage to your cover. The first problem you would notice would be a fading of any colored material in the cover so if you don't find any fading, then you shouldn't see any other problems.
  10. Of course, what waterbear said is right, but I thought I would tell you the main reasons that people tend to use bromine instead of chlorine in a spa. It's mostly that the chlorine in a spa outgasses more quickly than bromine so there is both more smell (the "clean" smell of bleach) and you need to replenish it more often. Generally, CYA is not recommended nor used in spas due to the higher disinfection requirements in a spa, because of the smaller water volume to people ratio (i.e. higher bather load) and due to the bacteria Pseudomonas aeruginosa which causes hot tub itch being so hard to kill. The high temperatures and high aeration in a spa along with no CYA (so high active chlorine concentration) means that half of the Free Chlorine can outgas in 24 hours. In a salt pool (3000 ppm salt for an SWG), half of the chlorine can be outgassed in 3 hours. Of course, one normally keeps a spa covered when not in use and that keeps the chlorine in the spa. waterbear, is the spa in your pool/spa open to air? Is the spa water always at 104F or thereabouts or do you just increase its temperature when it will get used? I assume you only have the jets on when you are using the spa so there won't be increased aeration all the time. Also, the half-life of chlorine that I quoted above would only apply to the chlorine in the spa portion in your pool and that would work out to be a fraction of the total pool volume so the loss might not be that noticeable (i.e. the rest of your pool volume is a large buffer of chlorine for your spa depending on the spillover rate). Also, since you use CYA in your pool I presume it must be in your spa as well. The bacteria Pseudomonas aeruginosa that causes hot tub itch actually thrives at 98F and can survive up to 108F so the typical 104F of a spa is quite cozy for this bug. A couldn't find a precise CT estimate for this bug, but it looks like its around 30-50 (probably at 77F) and other sources indicate that an FC of 2 ppm keeps this bug from proliferating. Of course that is all without CYA. At least for free-floating bacteria we know that it will get through your salt cell and be zapped at high chlorine concentrations at some point so maybe that's enough -- I don't know.
  11. waterbear, I believe the CT that dynamictiger is referring to is the standard product of chlorine concentration (in mg/liter or ppm) times the contact time (in minutes) and this product is approximately a constant at a given pH and for a given species of bacteria/protozoa/virus to be killed. dynamictiger, the standard CT tables refer to chlorine concentration without the presence of Cyanuric Acid (CYA). The values vary by pH with lower CT at lower pH because it is generally the hypochlorous acid, HOCl, form of chlorine that is effective as a disinfectant and not the hypochlorite ion, OCl-, form. What you may not be aware of is that in the presence of CYA, the amount of HOCl drops dramatically. A rough rule of thumb that applies at a pH of 7.5 and when the CYA ppm is at least 5 times the FC ppm is that the concentration of the active form of chlorine (HOCl) is reduced by a factor that is 75% of the CYA concentration in ppm. So at 30 ppm CYA, this means that the effective chlorine concentration (i.e. the number you use in the "C" part of CT) is reduced by a factor of 22.5 (in the example below, it's even worse at a factor of 34.5 -- I'll have to check if I need to change the rule of thumb, but the numbers below are accurately calculated and not from any rule of thumb). At the standard recommended NSPI values of pH 7.5, TA 100, FC 3, CYA 30, CH 300, TDS 550, Temp 80F, the concentration of the active form of chlorine (HOCl) is only 0.042 ppm (this is ppm in chlorine gas, Cl2, units as is standard with all chlorine measurements). Without the CYA, the active form of chlorine would be at 1.45 ppm or about half of the FC which is to be expected at a pH of 7.5. Now before you get too shocked from this info let me tell you what this roughly corresponds to in ORP terms. This roughly corresponds to an ORP of 690 mV. The standard ORP minimum requirement for disinfection in commercial pools in the U.S. is 650 mV (in Germany it's much higher at 750 mV) which roughly corresponds to about 0.013 ppm or an FC of 1.0 when the CYA is 30. However, this 650 mV ORP level for disinfection is lower than that required to kill "hard-to-kill" bugs (including the bacteria Pseudomonas aeruginosa that causes "hot tub itch") which is partly why CYA is not recommended for hot tubs. The 650 mV level is also lower than needed to prevent most algae. Data from users on another forum seem to indicate that at least 0.03 and usually about 0.05 ppm HOCl is needed to prevent green algae. Even higher levels, perhaps 0.07 ppm HOCl, is needed to prevent regrowth of established black algae. For shocking green algae, a minimum of 0.3 ppm HOCl seems to be required while mustard/yellow (and possibly black) algae may need 1.0 ppm HOCl. Though this does not sound like a lot of chlorine, and indeed it isn't very much if no CYA is used, it takes a LOT of chlorine to achieve these levels in the presence of CYA. Even with 30 ppm CYA, it takes about 12 ppm FC to achieve shock level for green algae and 21 ppm FC to achieve shock level for mustard/yellow (and possibly black) algae. If you didn't have CYA, it would only take about 0.6 ppm and 2.1 ppm respectively. I have all sorts of graphs and charts as well as a spreadsheet that computes the details of pool water chemistry, but it's on another forum and the rules of this forum seemed to imply that due to competitiveness no links should be made to other such forums (it didn't specifically forbid that, but it did say that those that run other forums couldn't post here; I don't run any forum, but don't want to violate the rules either).
  12. You mentioned in another pool forum that you wanted me to respond to this post, so I'm doing that here. I am not aware of the product these guys seem to be talking about, but a new plaster/gunite pool will indeed show a strong tendency to increase pH, especially in the first year and especially in the first few months after installation. The reason is that the process of curing concrete absorbs water and produces Calcium Hydroxide which is strongly basic (alkaline). So you will find that both your Calcium Hardness and your pH both rise over time though the rise in CH is smaller than the increase in pH and the amount of acid you need to add. There are other factors that cause the pH to rise in a pool, the most common being the outgassing of carbon dioxide which happens because pools are intentionally "over-carbonated" somewhat like a carbonated beverage (you do this by initially adding sodium bicarbonate to your pool). This is done to provide a carbonate buffer that reduces the amount of pH change caused by additions of acid or base to a pool and it is also done to provide carbonate ion so that when combined with calcium ion (which you add initially to a pool via calcium chloride) the pool is "saturated" with calcium carbonate (calcite). This is done to prevent corrosion of pool surfaces (and from grout in tile) while not being too much which would cause scale to form. This fine balance also coats some metal surfaces to inhibit corrosion though keeping the pH above 7.0 is generally a much more important factor for preventing the metal corrosion. However, this excess of carbonate in the pool means that it will outgas carbon dioxide to the air. When this happens, this is similar to adding base (alkaline) to your pool and the pH will rise (though unlike adding a base, the TA won't change). This process is accelerated at higher carbonate levels (usually higher TA), at lower pH and with increased aeration (e.g. waterfalls, spillovers, fountains). Using a pool cover, eliminating aeration features, keeping the pH at 7.5 or higher, and keeping the TA low (below 80, but don't go below 50), all help reduce the pH rise by reducing carbon dioxide outgassing. A pool that uses a salt-water chlorine generator (SWG) also shows a strong tendency to increase in pH and I believe this is due to the increased aeration of the water caused by the hydrogen gas bubbles that are generated (if you don't see such bubbles during the day, try running your pump and SWG at night with the pool lights on). It is also possible for some excess chlorine gas to be generated and not get dissolved quickly enough, but I find that unlikely. Some people have found that lowering their TA reduces the rate of pH rise which might seem ironic since a lower TA means less pH buffering but the outgassing forces from higher TA are a little more important than the buffering loss at lower TA. Some people have added 50 ppm Borates (from Borax; technically the 50 ppm measures Boron) to their pool which has significantly lowered the pH rise as well as chlorine demand. This is probably because they run at lower TA due to the Borates doing some of the pH buffering and the Borates are an algicide that lowers chlorine demand letting one lower the SWG production and therefore less aeration due to fewer hydrogen bubbles. So, back to your original question of this new "product". It could just be an additional buffer like the Borates. However, a pH buffer will reduce the amount of pH swing but it won't change the amount of acid you will still eventually need to add to restore pH. The buffer simply resists pH changes, but does so in both directions. So with a buffer, you may not need to add acid as frequently, but you will still need to add the same quantity of acid to get back to where you were. The exception to this is what I described above where the Borates have an additional benefit, especially for SWG pools, but that is not directly related to their buffering capability. The other possibility for their "product" is simply something that automatically adds acid to your pool. Perhaps they have come up with another slow-dissolving solid acid that doesn't have CYA (and probably doesn't have chlorine either). It is also possible that the "product" does something to isolate the hydrogen gas bubbles from the SWG generation so that they do not contact the pool water as much, but I doubt that this is what is done as it would be a one-time design change and not something you would have to buy every 6 months. It is also possible that the "product" is something that gets added to the water that is more easily reduced than water is to hydrogen gas (which is what the SWG does in addition to oxidizing chloride ion to chlorine gas) thereby generating less hydrogen gas so less aeration so less outgassing of carbon dioxide so less rise in pH. It would be tricky to find such a chemical since it can't be too easy to reduce or else the chlorine in the pool will oxidize it back to its original state, using up chlorine in the process (and it would have to somehow leave the pool or get converted into something else so that it doesn't get oxidized by the other plate in the cell). See if you can find out more details about this "product". [EDIT] P.S. I did a simple search on "pH stabilization pool" and found this link which refers to a SWG that also adds acid to maintain pH. However, what you described sounds more like a chemical addition than an automated pH detection and acid injection system. [END-EDIT]
  13. This is not true. When chlorine in water (hypochlorous acid, HOCl) is in the presence of Cyanuric Acid (CYA) it forms several chlorinated cyanurate species of which HClCY- (where "CY" is the cyanurate portion) is the dominant species. The reaction HClCY- + H2O --> H2CY- + HOCl has a half-life (at 77F) of 4.08 seconds. That means that it only takes about 4 seconds for half of the Total Chlorine (TC) to be made available as Free Chlorine (FC) as the Free Chlorine gets used up. In other words, the CYA acts as a buffer or reserve of chlorine and releases that reserve quickly in terms of normal demand. On the other hand, for the purposes of disinfection and oxidation, it is the concentration of the active form of chlorine, hypochlorous acid (HOCl) that is important. It is this concentration that is significantly reduced in the presence of CYA. At a pH of 7.5, a rough guide that is reasonably accurate when the CYA ppm is more than 5 times the FC ppm is that CYA reduces chlorine's active concentration, and therefore its effectiveness, by 75% of the CYA level measured in ppm. So with a CYA level of 30 ppm, the effectiveness of chlorine is reduced by a factor of 0.75*30 = 22.5 while at a CYA level of 100 ppm the effectiveness of chlorine is reduced bby a factor of 0.75*100 = 75. So, three times the CYA means 1/3rd of the chlorine effectiveness. Or put another way, you need three times the FC level with a CYA of 100 than with a CYA of 30 to have the same equivalent disinfection and oxidizing capability. So while the relatively large chlorine reserve means that there is lots of chlorine around to kill lots of bugs and algae (i.e. there is a large "capacity"), with high CYA and not high enough FC the active chlorine concentration may not be high enough to kill such bugs and algae at a rate faster than they reproduce (i.e. there is not enough "power" or "rate"). So having a high level of CYA does not prevent the chlorine from getting released. It just combines with too much chlorine leaving too little active chlorine. Though this can be compensated by higher FC levels, such higher FC levels result in higher chlorine usage since the breakdown from sunlight is related to this total FC level. I don't want to go into the details here, but I have lots of graphs and details about all of this on another forum, but this forum's guidelines refers to compeitiveness and preventing other forum owners from posting here. I'm not an owner of the other forum, but providing a link to it might tick off this forum's owners -- I don't know.
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