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There is ample evidence that high CYA causes corrosion and a need to adjust TA upward to compensate. See Taylor Test Booklet. For this reason I don't recommend regular use of dichlor in any body of water.
As told to me years ago by the late Jock Hamilton, founder of United Chemicals, and all around Water Swami, The dirty little secret of BCDMH (bromine tabs) is the H (hydantoin). Regardless of saturation, high levels of H will dissolve copper in the system. This is the big reason why we are instructed to drain and refill residential spas every 3 mos. even if not used. I've witnessed this corrosion and was stunned by how quickly it had wiped out copper heat sinks (does anybody remember those?). It only took about a year.
During the mid 90's Horner Equipment came to our site to do Beta testing of the Auto Pilot system on 2 commercial spas under our care that required monthly draining. They used sodium bromide only. We had no damage from corrosion afterwards. I have since moved away and don't have any facilities equipped like this, and can't provide up to date follow up.
It is my understanding that current recommendation is to combine chlorine and bromine salts for more efficient conversion of the bromide.
In summary, I think salt generation is, or can be, a huge problem solver.
Thanks for the reply. This is exactly what the PGN is all about. Your points are well taken.
Justin
Richard A. Falk said:
It is a misconception that the high pH of bleach and chlorinating liquid means that this causes the pH to rise in pools and spas. It does not take into account the fact that the consumption/usage of chlorine is an acidic process whether that chlorine usage comes from breakdown from sunlight or from oxidizing ammonia or an organic. The net result is nearly pH neutral. In fact, a saltwater chlorine generator produces the same chemical effects as producing chlorinating liquid or bleach including the production of lye (hydroxyl ion since hydrogen ions are removed to produce hydrogen gas). I describe the chemical details of this in my post at http://www.troublefreepool.com/post4367.html#p4367 . In spite of my using only 12.5% chlorinating liquid in my pool the pH is very stable only rising about 0.1 every month or two. I have an electric pool cover and that helps reduce outgassing of carbon dioxide which is the primary source of pH rise.
There is some "excess lye" in chlorinating liquid and some bleaches, but 6% Clorox Regular (unscented) has a minimal amount with its pH of 11.4 such that there is virtually no net pH rise from the bleach alone (off-brand "Ultra" bleaches typically have a pH of 12.5 with more "excess lye"). Of course, when you add liquid chlorine, the pH rises, but when the Free Chlorine (FC) drops back down from use the pH drops. In spas, some chlorine is outgassed and that part results in some pH rise, but overall if one keeps the TA low one can have fairly stable pH even in spas using bleach. This is because TA (at least from carbonates) has TWO effects: a pH buffer AND a source of rising pH from carbon dioxide outgassing.
As for Total Dissolved Solids (TDS) it very much depends exactly what the TDS is composed of in terms of knowing whether the water will develop problems. It is true that bleach, chlorinating liquid, and lithium hypochlorite add more salt than other sources of chlorine. ALL sources of chlorine increase salt levels because chlorine converts to chloride when it gets used up. For every 10 ppm Free Chlorine (FC), all sources of chlorine produce 8 ppm salt. Bleach, chlorinating liquid and lithium hypochlorite add an additional 8 ppm salt upon addition so their net increase is 16 ppm salt. However, increasing salt levels is rather innocuous -- consider that salt pools have 3000 ppm salt. Dichlor adds to Cyanuric Acid (CYA) and that is NOT innocuous and significantly reduce chlorine's effectiveness, slowing down its rate of disinfection and oxidation such that it eventually has organics build up faster than they can get oxidized (and in pools this is what leads to algae growing faster than it can be killed unless a supplemental algaecide or phosphate remover is used). If given the choice of CYA buildup vs. salt buildup, it's a no-brainer. People who have used the Dichlor-then-bleach method find that their water lasts at least twice as long as Dichlor-only and when they do change the water the difference between that "used" water and fresh water is less noticeable (i.e. they could have gone even longer). The definitive paper that determined the chlorine/CYA relationship was in 1974 and is in http://richardfalk.home.comcast.net/~richardfalk/pool/OBrien.htm .
You are right that supplemental oxidizers can reduce the need to use as much Dichlor and that reduces the rate of CYA buildup. However, ozone is a mixed bag since sometimes it ends up using more chlorine than it saves. I'm not sure why this occurs -- could be ozone oxidizing chlorine to chlorate or could be the aeration removing more chlorine from the water via outgassing. In pools and spas with heavier bather loads, the ozone probably saves chlorine by oxidizing more bather waste while in lower bather loads the ozone may use more chlorine as there is less else to oxidize (so the chlorine would have otherwise lasted longer).
As for salt systems, the pros are as you mentioned since on site generation of chlorine doesn't increase the salt level -- chloride is converted to chlorine and then reverts back to chloride. The main downside is the increased conductivity from the high required salt level that increases corrosion rates, but much of this can be mitigated if one is aware of the risks (there were other posts in this forum that talk about that). There is no perfect solution here -- each has its pros and cons in terms of side effects, cost and convenience.
Richard
I agree with most everything you said, however I question the use of liquid chlorine due to the use of caustic soda in its manufacturing process. I have always been of the understanding that it would add significant Total Dissolved Solids (TDS) to the water thus reducing the "life" of the water even further than sodium dichlor. The Cyanuric acid content in Dichlor is a valid point though and can be mitigated by using a supplement in the treatment such as ozone, ionization or various mineral "sticks" on the market all while reducing the need to use the Dichlor as often.
I used the Pioneer H2O system successfully for quite a while with zero side effects. I have also used other forms of sanitation that worked as well with out the added service issues of the Bromide salt system. There are many "green" systems for spas and many are wonderful with out raising the TDS levels or effecting the pH in any significant way. As a note* In my area of the country using a product that increases the pH is actually a benefit, to an limit, due to the low pH levels out of the tap.
Your thoughts?
Justin
Richard A. Falk said:
You do NOT want to use bleach-only because the active chlorine level is far too strong without any CYA to moderate its strength. It would wear on hot tub covers too quickly and would tend to dissipate faster. With around 30 ppm CYA in the water (around 33 ppm FC cumulative Dichlor addition) one has decent chlorine buffering and moderation of its strength.
The main thing to watch out for when using bleach or when using a saltwater chlorine generator (SWG) system is that the pH will tend to rise -- especially so in a hot tub with the high aeration. This can be significantly mitigated through having a lower Total Alkalinity (TA) in the 50-80 ppm range and through the use of 50 ppm Borates (e.g. via Gentle Spa which is mostly boric acid). TA is mostly a measure of bicarbonate in the water where pools and spas are intentionally over-carbonated to provide a pH buffer (and to protect plaster via calcium carbonate saturation) and the outgassing of carbon dioxide is what causes the pH to rise (with no change in TA, for technical reasons I won't get into here).
Also, when adding any concentrated chemical to a spa or pool, do so slowly over a return flow with the circulation pump running. This ensures thorough mixing. Otherwise, the chemical can settle to the bottom in concentrated form.
Richard
Maybe in a commerical setting or a spa that has very heavy bather load.
In the years that I used the salt system in a spa I have never had any of the issues that I have had in pools. I understand your statement of the transportation, but there is some truth to it. Another fact is, using a salt system in a spa will reduce your drain and refill considerably. Pioneer H2O recommends once per year based on TDS levels. Another nicety is the feel of the water, it is amazing over traditional chemicals. There are other "natural" chemical additives available that would give you a similar feel but the transport and water waste is still an issue.
The "Green" movement concern has some validity as well. There always going to be people that take advantage of a situation for their own gain, we can only hope that this is not a larger part of the industry. Sales hype is sometimes an opinion of a non-believer, it is not always an exaggeration by a sales person. Education is the best solution.
Justin
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