This thread is a response to posts in the thread Trichlor Tablet in Skimmer of Hot Tub and PMs from the now banned user HotTubTips. This user was banned due to an escalation that ventured into what came close to legal threats or warnings. I will address the issues technically in this thread, but the user will not be able to respond.
This is absolutely not true about bromine. Based on the PkData Hot Tub & Spa Consumer Survey, 50% of above-ground residential portable tubs/spas use chlorine (mostly Dichlor), about 32% use bromine, the rest use Nature2/MPS or "alternatives" (including those not EPA approved such as enzymes). As for manufacturers, not only do they recommend both bromine and chlorine, chlorine and bromine including Arctic Pure® Chlorine Tablets, chlorine or bromine, only bromine, chlorine or bromine, chlorine or bromine, and there are saltwater chlorine generators such as the ACE® system for Hot Springs.Originally Posted by HotTubTips
There is a misconception that bromine lasts longer, but with CYA in the water chlorine does not outgas faster than bromine. The main difference is that bromine comes in slower dissolving tablets that can be used for background dosing whereas chlorine needs to be added every day or two, especially if an ozonator is used since ozone reacts with chlorine (while with bromine, ozone can create more bromine from a bromide bank). Chlorine tends to be more popular than bromine primarily due to cost and to smell.
It is true that Trichlor tabs in a normal feeder cannot be used as it dissolves too quickly and that most manufacturers say not to use them, but as I noted in one link above there are some special dispensers that more slowly release Trichlor and even Aquafinesse™ is available with Dichlor powder or Trichlor tablets. Nevertheless, Trichlor should generally not be used in spas because it dissolves too quickly so if you overdose its acidity can damage spa components (the same it true in pools if you don't pay attention and test the pH and adjust it as needed, but one tablet takes days to dissolve so the risk is lower).
By the way, the following are chemical facts independent of concentration of product or of pool or spa size:
For every 10 ppm Free Chlorine (FC) added by Trichlor, it also increases Cyanuric Acid (CYA) by 6 ppm.
For every 10 ppm FC added by Dichlor, it also increases CYA by 9 ppm.
For every 10 ppm FC added by Cal-Hypo, it also increases Calcium Hardness (CH) by at least 7 ppm.
Note that Dichlor adds CYA to the water -- spa water -- and is the most common disinfectant used in residential spas. Of course, the buildup of CYA is the main reason the water needs to be changed as frequently as it does since it reduces chlorine's effectiveness to the point that the water turns dull/cloudy.
As I noted, Dichlor is the most popular disinfectant in residential spas. You are confusing state/county regulations that apply only to commercial/public situations vs. residential use. Obviously, state/county regs have to be followed for commercial and public pools and spas that fall under their jurisdiction, but such rules do not apply to residential use (and not all states ban CYA in commercial/public indoor pools or in spas). As for commercial/public use, obviously one does not want to overuse CYA, but the real ignorance is in not understanding how a modest amount of CYA moderates chlorine's strength enough to not be too harsh on bathers and enough to reduce disinfection by-product production but not so much as to prevent adequate disinfection. This is known science since at least 1974 (more on that later).Originally Posted by HotTubTips
Note that they refer to a buildup of CYA -- there is no buildup to high levels with the Dichlor-then-bleach method we propose. We only use Dichlor until the CYA reaches around 30 ppm and then switch to using bleach. Note how this is superior to what most residential spa users do which is Dichlor-only with CYA buildup. However, if you were to not have any CYA at all, then the chlorine would be too strong, would outgas too quickly, would degrade hot tub covers faster, would oxidize swimsuits and skin faster, would corrode equipment faster, produce disinfection by-products faster, etc.Originally Posted by HotTubTips
In the 2000 MMWR report about Maine, read the actual report about what it said:
The problem wasn't the CYA, though it was higher than the 20 ppm that should normally be used indoors with 4 ppm FC, but rather was little to no chlorine at all. Note that an FC of 4 ppm with a CYA of 20 ppm is technically equivalent to a pool with an FC of 0.2 ppm with no CYA. The EPA DIS/TSS-12 laboratory test requirements is equivalent to 0.4 ppm FC with no CYA at pH 7.5. The field test requirements are far looser as Trichlor was approved for use in pools and Dichlor for use in spas. Again, it is the overuse that is a problem so banning CYA completely for some uses shows ignorance. Remember that we are NOT saying to use Dichlor only in spas nor Trichlor only in pools -- to do so would increase CYA to high levels. What we are saying is to use moderate levels of CYA and use proportionately high enough FC levels such that the FC/CYA ratio that is proportional to the active chlorine level is sufficiently high for adequate disinfection (for pools, the level is enough to prevent algae growth which is higher than that needed for disinfection). And we are NOT saying to violate any regs for public/commercial pools or spas -- this is a residential pool/spa forum and such regulations do not apply.Chlorine and pH levels were maintained manually in the hot tub. To stabilize chlorine levels, 40--60 mg/L cyanurates were used. During the outbreak, free chlorine levels were tested daily and repeatedly registered <1.0 mg/L, less than the state-required level of 1--3 mg/L, in the pool and hot tub. The pool and hot tub were crowded during the outbreak, and free chlorine levels were very low to zero after the February 25--26 weekend; no measurements were recorded over the weekend.
I've spoken to both the head of the MAHC effort and to his CDC counterpart on the committee (I attended the NSPF WAHC last year and this year) and they now understand much better the chlorine/CYA relationship. Their main concern for CYA was in dealing with Crypto for superchlorination, but they are considering other alternatives such as use of chlorine dioxide (generated from sodium chlorite and chlorine) for overnight treatment.
I suggest one reads the "Chlorine/CYA Relationship" section in the first post of the thread Certified Pool Operator (CPO) training -- What is not taught. It gives numerous references to scientific papers explaining that relationship so that people no longer need be ignorant about the subject.
Again, the above shows ignorance for what CYA actually does and the public health references are for commercial/public pools and spas, though even so they still show ignorance of the actual science of the chlorine/CYA relationship. They all think that CYA's only role is to protect chlorine from sunlight and that CYA's reduction of chlorine effectiveness is so extreme that it shouldn't be used, but yet they do use it outdoors. The fact is that CYA is a hypochlorous acid buffer so one can tune the level of active chlorine one needs for appropriate disinfection and oxidation. CYA acts as a reservoir for chlorine so that you don't run out of chlorine which is something that is the primary reason for problems in the MMWR reports (there are a few reports with excessive CYA well over 100 ppm that are obviously problematic, but most are about near zero chlorine levels). CYA also moderates chlorine's strength. Using chlorine without any CYA can have the chlorine level be too strong. Europe understands this which is why their DIN 19643 standard targets 0.3 to 0.6 ppm FC with no ozone and 0.2 to 0.5 ppm FC with ozone in the circulation path. Higher active chlorine levels lead to faster oxidation of swimsuits, skin and hair and to faster creation of disinfection by-products. This is basic chemistry -- a higher concentration of a reactant results in faster reaction rates in whatever reactions for which the reactant participates.Originally Posted by HotTubTips
My wife has personally experienced this difference in chlorine's strength where in an indoor commercial pool she used to swim in every 5-month winter season we would have to replace her swimsuits every year and her skin was flakier and hair frizzier compared to our own outdoor residential pool she swam in for 7 months of the summer season where swimsuits would last for 7 years and the effects on skin and hair were far less noticeable. The chlorine level in the indoor pool was 1-2 ppm FC with no CYA, but in our outdoor pool it was 3-6 ppm FC with 30-40 ppm CYA but that is equivalent to around 0.1 ppm FC with no CYA. It is the factor of 10-20x difference in active chlorine concentrations that accounts for the different experience. Essentially, the indoor pool is significantly over-chlorinated in terms of the active chlorine level. Had the indoor pool used 4 ppm FC with 20 ppm CYA, it would have had an active chlorine level of 0.2 ppm equivalent with no CYA.
At this point, there were PMs from the user HotTubTips about legal issues including referring to the consultant Alison Osinski and her website statement about not using CYA in indoor pools or in outdoor pools or spas with high organic load problems. She has been an expert witness in many cases (not necessarily anything to do with chlorine/CYA -- she has degrees in Physical Education with a specialty in Aquatics, not in Chemistry). I've communicated with her before and though she never updated her website, she did understand the chlorine/CYA relationship to some degree. What she and Kent Williams at PPOA have not changed to see is that research has been showing how higher active chlorine levels lead to more problems with disinfection by-products. Blasting with high chlorine levels to provide faster oxidation has side effects and they are ignoring that. If there is liability to be had, that's where it is, and we're not the ones promoting it. Again, it's all about tuning the active chlorine level. In higher bather-load situations it is better to use supplemental oxidation rather than using only chlorine for that purpose. The active chlorine level should be set for providing consistent and adequate disinfection and CYA is an excellent way to do that since it's virtually impossible to keep 0.2 or 0.3 ppm FC everywhere in a high bather-load pool. This is why the CDC recommends at least 1 ppm for pools and 2 ppm for spas, but with CYA one can have higher FC level for a larger chlorine buffer while not having too high an active chlorine level. It's all about moderation in its use.
In addition to the links I referred to in the CPO thread, virtually every peer-reviewed scientific paper that looks at chlorine levels and disinfection by-products finds that higher chlorine levels (or chlorine to precursor ratios) have faster or greater production of disinfection by-products. This paper has Table 1 showing "tri" (trichloramine aka nitrogen trichloride) vs. chlorine dose. This paper stated that "The formation of trichloramine was strongly dependent on the Cl/P molar ratio…". This paper shows Figure SI-1 in the supporting info showing NCl3 vs. Cl:P ratio. This paper showed trihalomethane (THM) formation positively correlated with chlorine dose to DOC ratio. It is well known in the water treatment industry that higher chlorine levels lead to more chlorinated disinfection by-products. Of course, if one does not remove the chemical precursors from the water, then they will still eventually react with the lower chlorine levels, albeit more slowly, but a lower active chlorine level will react more slowly with skin when you are in the pool and some of the precursors will be removed through coagulation/filtration, outgassing or dilution.