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  Richard A. Falk January 10, 2012 at 5:17pm

  Thanks Clemente.  So now we're agreeing on more points.  Yes, it's all about getting enough chlorine fast enough to where it needs to be, so to the degree that good injection and mixing helps with that, then the results will be better.  And with faster more thorough mixing throughout the pool, the responsiveness will be faster so ORP will be closer to measuring what is really going on rather than some time-lagged guess of "what is" based on "what was".  As I wrote to Al in my last post, HCF can help make ORP better for the reasons I just described.  I'm still concerned about using ORP as an absolute standard because those links I gave to you are STILL the current manufacturer measured values of their ORP sensors in reasonably clean water and they are all over the map.  Those tables weren't based on bad mixing in large pools with high CC or anything like that.  Of course, they probably have not updated that information in quite some time, though they should.  At least in a pool with HCF, your FC values will be making some sense relative to ORP.

  For outdoor pools exposed to sunlight, HCF allows for faster responsiveness to chlorine loss from sunlight, but unless you are able to keep the chlorine level very low in the 0.2 to 0.5 range, then you will be using more chlorine (and producing more disinfection by-products that don't show up as significant CC as I had mentioned earlier) than if you had an FC of 4-6 ppm with 20-30 ppm CYA, for example, and the higher FC allows for plenty of chlorine buffering to handle localized bather load.  Of course, in New York, you have no choice due to regs.
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  Clemente Rivera January 10, 2012 at 4:32pm

  Richard:

  I was typing my prior comment as you chimed in...

  I was talking with some pretty good authorities on the subject of ORP, and we were able to deduce the following...

   

  ORP sensors today are much more reliable than ever before - self cleaning, better electrolytic gels, and improvements in the flowcells make for this - so reliability is definitley high, unless your pool is a swamp...

  The FAC levels dropping after two weeks on HCF is actually opening the eyes of some controller companies...

  "Every Pool has a different ORP value" - this was the case for years - Now HCF is literally putting these pools in check...All my HCF installs have "Broken the rules" of controller operation...

  -Outdoor pools running on PROPORTIONAL FEED & maintaining within 1 MV of setpint during High Sun Times (NO CYA - FYI) - "NO WAY", says the Controller Companies - but they have well documented reports from my happy customers.

  -Every pool plays with the SAME ORP level and gets the same results - NO WAY - they say again...

  Yet now they see the trend, and now they are all ears...

   

  Know why all pools have varying ORP levels? Try this - Mixing at each facility is slightly different...

  Injectors connect to straight pipes to the returns usually have higher ORP setpoints to maintain a given residual, while Injectors with elbows between them and the bulk water will mix a little bit - and the HOCL process works a little better, leading to lower ORP for the same Residual....

  ITS ALL ABOUT THE MIXING....

  And guys, Im not done there - Im working on a little surprise to prove my point... in the works, and will let you in on it as the project unfolds...

   

   

   
• 

  Clemente Rivera January 10, 2012 at 3:31pm

  SMH - Ill tell you what - Im going to install this equipment, and make a contribution to the pool industry by helping IMPROVE Bather Comfort, and reduce Operator's Pain...

  We can go on forever and not get anything done.

  I believe the system works.  Its obviously doing something that some people cant explain - and thats the reason we are having this discussion...

  by the way - the feeders in my demo will be EQUALLY sized.  I didnt want that to become an issue.  equal feed rates, only because of my earlier comment about being able to add bigger pumps, but not getting the same result...

  Goodnight...
• 

  Richard A. Falk January 10, 2012 at 3:25pm

  Al, just so you know, we are even in more agreement than you indicate.  The list I gave of possible reasons for varying FC/ORP correlations is not the same in the before and after scenarios.  It's more like what you wrote about the water getting cleaned up.  The interference, in giving an artificially "too high" level for FC, can occur when there is more CC so in the "before" case, but not in the "after" case where CC has been reduced or effectively eliminated.  ORP sensor fouling may also be higher in the "before" case than "after" due to more contaminants in the water that aren't getting oxidized quickly enough in the "before" case.  The slow response to bather load in terms of providing enough chlorine where needed is clearly worse in the "before" case than "after".

  There might be another factor in terms of how CC or contaminants in general affect ORP readings.  They are not oxidizers and may not be reducing agents, but nevertheless might react in some way with the ORP sensor to affect its readings.  This is speculative, but could be an additional explanation for how ORP levels vary in waters with the same FC levels (and pH, etc.).  Technically, if there were no interference in the FC test, then the HOCl level would not be lower at a given FC and pH in the presence of CC though obviously it may drop over time if not replenished.  The fact that ORP readings are lower relative to FC either means that the FC test has interference (i.e. reads artificially too high from the CC) or that the ORP is reading lower in the presence of CC.

  As for my ORP discussion, that was only in response to Clemente's "zero FC, but good ORP" comment.  My point was only in trying to use ORP as an absolute standard, not in its use as a relative standard for process control.  In fact, with HCF enabling enough chlorine to get to where it is needed more quickly, the use of ORP for process control becomes easier and more reliable, as you have noted.  I'm all for HCF, but let's stop this "more HOCl" nonsense when it's really about rapid responsive chlorine delivery and proper dispersion to get it where it is needed most.
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  Al Neumann January 10, 2012 at 2:31pm

  Clemente:

  You asked me to chime in…so I will. Are we on the same planet?

  It appears to me that in objectively reading Richard’s last  comments, (not so much his last one on ORP), and your last couple of comments, that Richard has more of a handle on what HCF is all about much more so than you…at least that’s my perspective…because he is basing what he is saying on chemical principles rather than apparently throwing stuff on the wall and seeing what sticks.  Many of your statements have some truth in it as pertaining to what you are seeing that I totally with, but you then corroborate it by making statements that literally don’t make any sense as being the reasons for the positive changes you are seeing…Oftentimes when I read some of your comments I say to myself…OK…yaaa, to a point…and then…WHAT!!!

   

  I think I need to start from the beginning on this and get this on square one. Do you understand the equilibrium role that pH plays with HOCL and OCL^-? You see this everyday if you have a 1 mV ORP controller. When the pH goes up, the ORP goes down. When the pH goes down, the ORP goes up. Pour some acid in the surge tank and see what happens.

  I need to know, yes or no, that you understand and agree to this.

  If not, then do you have another explanation for this that bypasses this equilibrium that is rational, and chemically makes some common sense, and not just some made up mumble jumble that sounds good? You can’t just keep on throwing out irrational statements, and claiming them as proof, and expect anyone to have clarity and say…oh, that’s why.

  If you say yes, then everything I said, and what Kim said, and much of what Richard has said, goes against your theory of HOCL dependence on how it is injected into the pool.

   

  The other thing you are not mentioning here is the amount of chlorine being fed...the  dosage. These feeders are designed to be used with proportional feed control, so based on how you often set things up, the feeder is on for about 20 sec every 2 minutes for when the ORP is 1 mV below set point, and maybe on for 30 sec if maybe 5 mV off set point, which is hardly ever. Yes we are putting in a lot of chlorine during that time span. However, it is done to allow for faster mixing, enhanced by the injector, for the chlorine to diffuse throughout the pool and get back to the sensors to turn things off...not for HOCL production in the pipe...alas, the combination of the wait time of the proportional feed.

  There physically is not enough time that the chlorine is being fed into the bypass for it to do be the entire basis for some of the things you are arguing about. Taking into the account the Law of Dilution time-frames, and that we are on a 1.25” bypass, and that we are using a feeder that is designed to be off FAR more than it is on, goes against your argument by logistics if nothing else.

  It’s all about potentials, not absolutes. It’s all about reductions, not eliminations. It’s all about meeting any demand in a timely fashion, and increasing the pool’s response time…yes, starting at the point of injection, but not limited to just the bypass and return piping.

  You mentioned:

   With ORP/PH remaining constant, the fac drops after about a week after the equipment is installed. I have never let it drop below 1ppm, simply because health codes mandate it.

  
  I have to agree with both you and Richard on this, as both of you can appear to be right on this point. If the ORP /pH are constant, via set points, then as the pool is cleaning up, I would expect the FC readings via DPD, to get lower because more FC is available in its various forms depending on pH. On the same token, if as Richard stated, if the FC were constant, then as the pool was cleaning up, I would expect the ORP level would rise, as there is less oxidation needed. It’s a matter of semantics and what you want to control.

   

  You then mention:

  Whats making the free chlorine level drop? An amount of HOCL that we cant measure. The drop in fac is simply due to the obvious production of HOCL, which proves that the mixing concept is working. The reduction of fac levels indicates that the ORP IS NO LONGER TRACKING THE FAC LEVEL- ITS TRACKING THE HOCL PRODUCED.

   

  I think I understand what are saying, but I’m not sure if this is the correct way of saying it. The statement “The drop in fac is simply due to the obvious production of HOCL” is due to; as the pool is cleaning up, the HOCL portion of the FC is not being used up as fast as before, so is a bit more powerful, in a smaller quantity in oxidation potential, as measured by ORP. To say that it is due to HOCL production caused by mixing in the pipe only, as you propose is again hampered by sheer logistics.  

  To say that “ORP IS NO LONGER TRACKING THE FAC LEVEL- ITS TRACKING THE HOCL PRODUCED” followed by your discussion of 0 FC and ORP is confusing at best.

  I understand Richards’s bullet list of potential reasons for lower FC levels, but those are true in either before and after scenarios. With those as a constant, Richard is hung up on the viability of ORP in general, so there is a bias there. This is not the time for this specific discussion to take place, because he is well entrenched in his take on this. All I will say is that the sample is tested by the sensors, and the before and after sensor readings are with the same sensors, so tracking improvements are correlated to the quality of the water.

   

  What’s important here is what is getting lost in this type of rhetoric.

  There are over a thousand units out, and I would say that 99%, (let’s say most) have noticed significant improvements in both air and water quality over what they had before, simply by using liquid chlorine a little bit smarter. Notice I said improvements, caused by reductions, not absolutes such as eliminations. I don’t agree with hardly any of your reasons for this that you have manufactured, but that doesn’t change that something positive is happening in the main body of water that is indicated by our patrons noticing improvements over what was.

  I for one will await your video, although I suspect it will do nothing except to show the difference in feed rates and mixing of conventional feeders vs the HCF feeder. Yes, it will probably show enhanced mixing, both in the pipe and in the main body of water. But will it prove anything for this HOCL theory?…not a chance.
• 

  Richard A. Falk January 10, 2012 at 11:49am

  Quite frankly, if you were in fact measuring FAC using DPD taking a water sample at the ORP sensor and quickly measuring it and found it to be zero, but were relying on the ORP value that seemed to be OK, then that is very dangerous and you should consider the ORP sensor to be very suspect.

  ORP is notoriously flaky and is NOT an absolute standard in spite of what some people may say.  Even the manufacturer's own specs show not only vastly different ORP readings at the same FAC levels, but they even vary in their slope (i.e. mV change for every doubling in FAC).  For example, Sensorex shows a ridiculously high 84 mV per doubling in FAC while Aquarius Technology shows a 46 mV per doubling in FAC while Chemtrol (SBControl) shows a 22 mV per doubling in FAC while Oakton shows a 28 mV per doubling in FAC.  The post/link where I show Oakton also demonstrates how 130 of the measured pools had additional ORP sensors built-in and where the Oakton and those sensors differed by more than 100 mV in 23% of those pools with no apparent correlation (i.e. it wasn't just a bias difference between the two sensors).

  Using ORP for process control via a setpoint you manually set to correlate an ORP reading with an FAC reading is one thing, but relying on ORP as an absolute measurement is very dangerous.  It can give you a rough idea for other things to look at, but is too inconsistent, can be fouled too easily and is fooled by too many substances that are not strong disinfectants or are too selective oxidizers.  This post pretty much sums up the futility of relying on ORP for anything but approximate process control.
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  Richard A. Falk January 10, 2012 at 10:50am

  I did not write "The Dpd testing does NOT TEST FOR HOCL".  I wrote that the DPD test does not test for ONLY HOCl.  It tests for all chlorine that can become HOCl quickly, so includes HOCl as well as hypochlorite ion (OCl-) and chlorine bound to CYA (since it is released quickly in the time of the chlorine test).

  As for the FAC dropping at the same ORP level, that should be looked at the other way around.  At the same FAC, the ORP level is rising after use of your equipment.  It's amazing to me how you can take an observation and force-fit it into an explanation that works to support what you want to believe.  There are many different possible explanations for what you are observing, some more likely than others.  I list some of them below, with the most likely ones first.

  • Interference in the Free Chlorine (FC or FAC) test from either organic chloramines (specifically, N-chlorinated amino acids and N-chlorinated heterocyclic compounds) or from high levels of monochloramine.  Either of these can at least partly measure as FC even though they should be measuring as Combined Chlorine (CC).  Since before your equipment you were measuring more CC, then this bleed-through CC interference in the FC test is the most likely explanation.  See this document for more technical details.
  • Dirty ORP sensors or other ORP interference.  It is known that many substances affect ORP readings, not only directly but also indirectly through sensor fouling.  For example, this can be a problem when CYA is used since it lowers the HOCl level and therefore the ORP mV reading into a noisier and more sensitive range, but other organic substances can also foul the probe when materials accumulate in a thin film on their surfaces.  See this article for more non-technical info.  Some of the CC you were measuring before use of your equipment may have been fouling the ORP sensor.
  • Slow response of chlorine introduction to increases in bather load before your equipment is used.  This can lead to a lowering of FC as bather load uses up chlorine and produces more intermediate CC.  Then, the older equipment eventually senses the drop in ORP, but overshoots having the FC be higher than needed, especially after bather load has subsided.  Unless you are measuring the FC where the ORP sensor is located and depending on when you are doing the measurement with respect to this undershoot/overshoot, you can end up with uncorrelated FC/ORP readings.
  • Variation in pH.  I assume you are maintaining the same pH before and after use of your equipment, but if you are not (especially in the area of the ORP sensor), then the ORP level is sensitive to pH, even beyond the dependence of HOCl concentration on pH.
  • It is possible, though unlikely, that before your equipment there are organic substances in the water that behave in a similar way to CYA that bind to chlorine, but release it quickly enough to be measured in the chlorine test and that your equipment is somehow able to remove such substances.

  You wrote "ORP IS NO LONGER TRACKING THE FAC LEVEL - ITS TRACKING THE HOCL PRODUCED".  This is not true and has never been true.  ORP does not directly track HOCl, but is roughly correlated with it.  However, ORP is a net electrochemical measurement of ALL oxidation and reduction substances in the water, not just HOCl (I already noted earlier how hydrogen gas and MPS can both interfere with ORP readings, but they are far from the only substances that can do so).  You would need to get an HOCl specific sensor, such as a membrane-selective HOCl sensor or an amperometric sensor in order to directly measure the HOCl level.  You cannot conclude anything definitive about HOCl by just looking at ORP vs. the DPD test since ORP is affected by chemicals and factors other than HOCl while the chlorine FC/FAC test can also be interfered by other substances.

  In your example where the FAC level is down to 0 but the chlorinator is still feeding and maintaining a steady ORP level, you are either not measuring the FAC where the ORP sensor is located so have a physical mismatch of FAC levels in two different locations or the ORP is measuring substances other than HOCl or you have a time lag in measuring the FAC with the DPD test.  HOCl itself will always get measured in the FAC test, at least for the water sample you are taking at the time you are adding the DPD indicator dye.  However, it is possible for the FAC to drop as it continues to react with what is in the water (say, ammonia from bather load) if you wait too long to do the test after removing the water sample.  The ORP is taking a more immediate reading without the delay.

  You are simply wrong, wrong, wrong about DPD not telling you about HOCl in the water.  If there is HOCl in the water, then it will be measured in the DPD test along with all of the reserve chlorine (hypochlorite ion, chlorine bound to CYA) along with some interference from some types of CC, notwithstanding the time delay issue I just mentioned.  If you have higher ORP and have eliminated sample location and time delay as factors, then you need to look elsewhere for explaining the higher ORP reading.

  Since you are so focused on HOCl, I strongly suggest you buy an expensive membrane-specific HOCl amperometric sensor such as the Hach 9184sc Hypochlorous Acid Chlorine Amperometric Sensor or the Omega FCLTX if you want to know the true HOCl level instead of trying to use ORP as a poor proxy.
• 

  Clemente Rivera January 10, 2012 at 5:02am

  Thank you for the explanation...
  
  Now...with your statements in mind...i want to indicate something that has become clear to me.
  
  The Dpd testing does NOT TEST FOR HOCL.
  
  I am now aware of something...
  
  Al: if you are reading this...pleaze chime in...
  
  Ok. Al and I have been trying to understand a phenomena that has been occuring with these systems...
  
  With ORP/PH remaining constant, the fac drops after about a week after the equipment is installed. I have never let it drop below 1ppm, simply because health codes mandate it.
  
  Whats making the free chlorine level drop? An amount of HOCL that we cant measure. The drop in fac is simply due to the obvious production of HOCL, which proves that the mixing concept is working. The reduction of fac levels indicates that the ORP IS NO LONGER TRACKING THE FAC LEVEL- ITS TRACKING THE HOCL PRODUCED.
  
  THIS CAN BE PROVEN...ONE...LET THE FAC LEVEL GO DOWN TO 0, AND THEN EXPLAIN WHY THE CHLORINATOR IS STILL FEEDING, AND MAINTAINING A STEADY ORP LEVEL? ITS BECAUSE AT THAT POINT, THE ONLY THING BEING INTRODUCED IS HOCL FROM THE FEEDER. MY ISSUE IS, I CANT TELL YOU HOW MUCH, BECAUSE 1) DPD ISNT TELLING ME HOW MUCH HOCL IS IN THE WATER.
  
  SO, INCREASING THE ORP LEVEL TO MAINTAIN A RESIDUAL FOR THE HEALTH DEPT IS NEEDED...BUT HOW HIGH? I DONT THINK THAT A 2.5 PPM RESIDUAL (FROM DPD) IS REQUIRED...
  
  So...if we are all in agreement...HOCL PRODUCTION is the advancement that HCF gives us. We are using our chlorine the way it was meant to be used. At this point ORP measurement is the only way to guage this, unless an HOCL TESTING METHOD is introduced.
• 

  Richard A. Falk January 10, 2012 at 4:01am

  Clemente, you were the one who kept on bringing up HOCl and how HCF was producing more HOCl, etc.  Your initial statements were that "In order to ensure that your chlorine is fully converted to HOCL, you have to properly mix your chlorine into the water." and "Now, you can dose your chlorine properly, and ensure that 99.999% of the chlorine injected is converted to HOCL."  When using hypochlorite sources of chlorine, those are simply false statements since until diluted into the bulk pool water, most of the chlorine is hypochlorite ion, not HOCl.

  Dosing chlorine from a capacity or reserve point of view is based on Free Chlorine (FC) sometimes called Free Available Chlorine (FAC).  However, not all FC is active chlorine, that is hypochlorous acid (HOCl).  Some of it will be hypochlorite ion (OCl-) and in fact most of it will be when the pH is high as is true for hypochlorite sources of chlorine until they get diluted all the way down to the bulk pool water at pH 7.5 where half is hypochorite ion and half is hypochlorous acid.  By the way, unless the pH is very, very low, VERY little chlorine is "elemental" which I presume you mean Cl2 or aqueous chlorine (basically, dissolved gas) since it combines with water to form hypochlorous acid and hydrochloric acid which is the equation you had in your initial posting.  However, you left out other equations of equal importance:

  HOCl <---> OCl- + H+

  Hypochlorous Acid <---> Hypochlorite Ion + Hydrogen Ion

  HOCl + H2CY- <--->>> HClCY- + H2O

  Hypochlorous Acid + Cyanurate Ion <--->>> Chlorine Bound to CYA + Water

  At high pH, the first reaction shifts way to the right.  At pH 7.5, it is roughly balanced 50/50.  The second equation represents what happens when CYA is in the water where at typical pool pH it is mostly shifted towards the right (the "H2CY-" is the CYA core, which at pool pH is mostly cyanurate ion).

  All standard chlorine tests, be they OTO, DPD, FAS-DPD, are all measuring FC aka FAC.  They measure the chlorine RESERVE (plus HOCl), and NOT only HOCl.  Even though HOCl is what oxidizes the dye or the titrants in the chlorine test, hypochlorite ion quickly produces more hypochlorous acid well within the time of the test so you end up measuring hypochlorite ion as well.  When there is CYA in the water, then the chlorine bound to CYA gets released reasonably quickly, well within the time of the chlorine tests, so you measure all the chlorine bound to CYA as well.  So if you want to know the active chlorine level, you cannot look at FC (FAC) alone.  You have to also look at the pH and the CYA level (if present) and do appropriate calculations.  ORP is better correlated with HOCl, though is also interfered by other factors not relating to disinfection or really to oxidation in a practical sense.  For example, hydrogen gas bubbles from saltwater chlorine generators can end up affecting the ORP sensor making it read artificially low.  MPS can make it read higher even though MPS does not disinfect nearly as quickly as HOCl (though MPS is an oxidizer, though like HOCl it is selective).  There are some membrane-selective HOCl sensors available as well.

  However, oxidation rates depend on the concentration of the oxidizer (normally HOCl) and disinfection rates depend on the concentration of the disinfectant (mostly HOCl) and NOT on the amount of chlorine in reserve.  The hypochlorite ion, as well as chlorine bound to CYA (if present), should be seen as reserve chlorine that is not "active".  It is released as needed, but does not directly contribute to reaction rates.  Think of it like active soldiers on the front line with many reserve soldiers in the rear.  If only the front-line soldiers are doing the killing of the enemy (oxidizing or disinfecting), then it doesn't matter how many soldiers you have in reserve nor how quickly they can replace a fallen front-line soldier in terms of the enemy killing rate.  The size of the reserve just tells you how long you can continue to fight until you provide more reserves.

  Was that what you were expecting?  HCF has absolutely no effect on shifting any equilibrium chemistry more towards HOCl.  All it can do is two things: 1) have high feed rates to quickly add chlorine to meet chlorine demand from changing bather load and 2) mix the chlorine into the water faster.  It cannot change the relative amounts of HOCl vs. OCl- in the bulk pool water and as I wrote earlier, even with mixing "in the pipe", the pH remains high enough to have HOCl not be anywhere near the FC (FAC) level when using hypochlorite sources of chlorine.
• 

  Clemente Rivera January 10, 2012 at 3:35am

  Im a little confused...now youre telling all of us that the calculations for dosing chlorine are not correct?.
  
  I simply calculated the increase in ppm FAC (not Hocl) in the pipe based on how much chlorine wass going in, and the water flow...there are no smoke and mirror tactics here...if you put 1a GALLON of fresh bleach into a pool of given size, you get x ppm of fac, am i correct...i want to be specifically clear here...
  
  I have a question for you...
  
  Dpd testing: are we testing fac in elemental chlorine form, or are we testing fac in the form of Hocl?
  
  I know the answer already, just want to see what you are going to tell me...