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  3t94l0x1hbw8f November 11, 2009 at 3:53pm

  I just got in on this one and everyone has posted a lot of good ideas. All I can add is this: Turn off the edge late in the day, test the chlorine in the pool and the surge tank (presumably they will be equal). The next morning, test them again - a large difference in the readings bewteen the two would suggest that one-or-the-other vessel has something consuming chlorine. My bet is that the surge tank will have a big chlorine drop compared to the pool itself and something about the surge tank is the culprit. Please keep us advised.
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  Wes Burdine November 9, 2009 at 11:35am

  What types of Chlorine are you using? What is the TCL vs FCL? Ph? Alk? Temp?
  
  Have you tested the TDS? There has to be something in the water using up the Cl. As TDS increases, the amount of partially oxidized and unoxidized organic contaminants also increases. Much of this is uncharged or neutral and therefore will not contribute to measurable TDS . This added material will however increase in the consumption of your disinfectant by fueling growth rates of algae and bacteria. Suffice it to say, when the TDS is high, the organic contamination can also be seen to be high. Is this a new issue, or has this been the case yr. after yr.? It may be a case of the old "tired" water, and a dilution will solve the issue.
  
  Since you are treating for Phosphates, more than likely because high end clients also use a landscape service which fertilizers on a regular basis, you need to be testing for Nitrates also. My best guess is if the chemistry is balanced, then Nitrates are the culprit, if in fact the phosphate level is in check. Either way, both should be addressed.
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  John Gable November 9, 2009 at 9:31am

  Does the surge tank have an enclosed top or lid? If so bacteria, algae or mold and mildew can grow on the underside because it is not “IN” the water. I have even seen algae in a surge tank on an indoor pool. The high humidity is a fertile breeding ground and could cause the wide fluctuations in the pool chlorine level you described.
  I am also very negative on CYA. Be sure you get a chart that shows the affect the CYA level has on actual usable chlorine and the influence of the pH.
  BePoolSafe
  John Gable
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  Steve Dunn November 9, 2009 at 9:17am

  The surge tanks do not cause a loss of chlorine. The vanishing edge may cause a little more loss of chlorine than normal. Test the water for phosphates and nitrates.
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  David Penton November 8, 2009 at 9:24pm

  I looked at the pictures... Like someone else suggested, make sure that the gutters are free of any organic materials (dead lizards etc.).
  
  Second question is: Are you having a problem with algae growth in either pool? I have seen 2 times in the last 16 years similar situations, where there was no chlorine reading, but the pool water was pristine, and looked to be fine. Both these pools were pools we began to service after the homeowner had been doing it themselves. In both cases, for about 6 months the pool stayed perfectly clean and clear, yet we never had any residual on our test kits. Then over the course of about 4 weeks, the readings on our test kits "came back". It was almost like something was "masking" the actual chlorine readings we were taking in the field.
  
  I also have had another situation where at the same time EVERY year (for the past 15 years) we have a period of about 4 - 6 weeks where we cannot keep any chlorine in one particular pool. My service guys add 2-3 gallons, and fill 2 floating tab feeders with tabs, and the homeowner adds 1 gallon of chlorine every 3 days to keep the pool from "flipping". In this case we think that the VERY LARGE tree in the backyard is going through some sort of annual cycle which is shedding some sort of organic "something" which is very quickly using up the chlorine. This particular pool will go like this for a number of weeks, and then all of a sudden we will walk in to a pool with a 5.0++ chlorine reading one week, and we know the tree has finished doing it's thing.
  
  Maybe 1 of these will help you in your troubleshooting... Good luck! These can be a real pain; especially with very high end clients.
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  Timothy Robinson November 5, 2009 at 9:51am

  Pictures of the 2 pools

  IMG_0298.JPG

  IMG_0375.JPG

  IMG_0192.JPG
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  Timothy Robinson November 5, 2009 at 9:43am

  The pools are in fact "wet edge" pools, one is pebble and one is tile.
  We have decided to set up a project to hopefully prove our hypothesis which is that the constant spillover and aerated water causes chlorine to off gas much more rapidly.
  
  We will set up the project over 14 days. The first week we are going to leave everything running as normally programmed and document all chemicals each day and also everything we add (the amount of tabs or shock) to the pools each visit. We are hoping that the chlorine will go down each day that the negative pump is running.
  At the start of the second week we are going to turn the negative edge pump off and again document all of our chemical readings each visit. Hopefully we will be able to conclude that the constant spillover is off gassing chlorine much faster than when the water is not spilling over.
  I will post an update with the results.
  
  Thanks again guys!
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  Bruce Hudson November 3, 2009 at 5:40am

  Timothy,
  
  While testing the water, take a look at nitrates too. There is some reason for these two pools to not hold chlorine, and I would bet you have dozens of other neg. edge pools that do just fine.
  
  A chlorine-demand test may also be informative. You said the edge goes all around. Are you describing a wet-edge with a semi hidden trough? If so, close inspection and flushing may be in order
  
  I now recommend 2 speed or variable speed pumps run on low rpm 24 hrs on neg. edge and wet edge pools for a number of reasons and see no change in the pools' ability to maintain a residual.
  
  What is the water temp? Are these pools dark colored? Scottsdale gets a little warm :) Areating water over the edge should have a cooling effect, I would think, but once the water hits about 90 deg. chlorine goes away quickly.
  
  Happy hunting and good luck.
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  Timothy Robinson November 2, 2009 at 2:17pm

  We agree that the water constantly spilling over is one likely cause of the problem, we just don't know why or how to prove that? Both pools actually run the negative edge pump 24/7 as well, It was recommended by the builder that they run all the time and they are both wealthy clients that like to see them running so I don't think turning them off will be an option.
  The Builder recommended they run all the time because of the temperature change between the wall and the water having
  a weathering effect on the life of the wall.
  Anyways, I don't believe their are high phosphates in the pool because we have our guys treat phosphates regularly but I will have to check on that.
  
  Thanks Guys
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  Bruce Hudson November 2, 2009 at 1:40pm

  Don't know why, but phosphate removal often helps these cases where a pool will not maintain a residual. Assuming stabilizer is ok and there is not a huge organic load which it looks like you've already addressed.