Considering Conversion to ORP using liquid chlorine and O2

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D

dmccarthy

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Aug 8, 2015
65
Jeffeson, MA
Just changed out the water in my 24,000 gallon, commercial, gunite indoor pool which we were previously using bromine tabs through an off-line automatic brominator. For a lot of reasons (the most being the accumulation of DMH over time). I also just installed a paramount UV-sanitizer sized for the pool and have it set to run during the day while bathers are in the water. I also purchased and installed an in-line zinc anode as well. So far I am just using liquid chlorine to sanitize and adding small amounts of dry acid to control the pH and try to keep everything at 7.4-7.5. The water has only been changed for about 1 week and I am looking for alternative sanitization systems. I would rather not use a SWCG due to potential problems with my concrete deck and corrosion of our ADA pool lift, lights fixtures which are old, etc., and was looking into an ORP-based system that uses liquid chlorine and O2? Any suggestions would be much appreciated as I would rather not start using the brominator again as I would have to shelf this until I changed the water again.

Thanks in advance!
 
Since it's an indoor pool and as long as you keep the CYA low, ORP should work. There are a few dosing systems for bleach, or you could make your own with an ORP controller and an injection pump.

I'm not sure what you're thinking on the oxygen part of that?
 
Sorry meant CO2 not O2..typo. Would prefer CO2 vs muriatic acid to control pH, but open to suggestions for or agianst either. I have a small filter room with a gas heater and would rather not have liquid chlorine and muriatic acid in the same general area or potentially 2 competing liquids within relative close proximity to eachother. But again, open to suggestions for or against either.

Thanks
 
A CO2 injection system is fine for a commercial pool as long as you have good access to CO2 delivery. Definitely stop using the dry acid though, sulfates are bad for concrete.

I think an ORP system will work just fine for your pool BUT please don't rely on it as your only check. Nothing replaces a good solid DPD-FAS test kit for measuring exact FC/CC levels. ORP probes can get flaky over time and need replacing. Next thing you know, it fails and you've got no chlorine or too much chlorine in the pool. In fact, if I were operating your pool, I would find out from the manufacturer exactly what the expected lifetime of the probe is and then just make sure you replace them on a scheduled interval rather than wait for failure. Perhaps the probe supplier has a buy-back program where they can take back old probes, refurb them and that way you have a known source of ORP probes. I would do the same with pH probe - scheduled, preventative maintenance rather than failure detection.

- - - Updated - - -

Did you ever find out if using CYA is allowed in your pool?
 
Thank you for the info. That would make sense to have the sensors on a regular replacement schedule if I decided to go that route and not wait until one fails. Currently I have a back-up replacement motor in case our pump ever goes which they seem to do every few years running constantly. We do also (and are required) to test with the a DPD-FAS kit and I use the taylor one currently recommended by this site. We have to record our testing 4x/day and keep a record of and when the inspector comes out annually he usually sequesters a few weeks worth of documentation. I will have to look into CO2 delivery access. One of the pool companies said I could buy the tanks from them and then get the CO2 filled myself which he said would be cheaper, but it also sounds like a lot of work and ideally (if the cost is not outrageous) I would prefer to have someone deliver/fill on a schedule if possible.

As far as the state regs for CYA in an indoor commercial pool I have found no other documents than the one that exists that says it is allowed up to 100ppm for commercial pools and nothing specific for indoors. I could have sworn someone (whether the inspector or CPO course I took) told me it was not allowed in the state. I did talk to the CPI who taught one of my CPO courses and he recommended that I do not add CYA to an indoor pool, but he did not really offer up as to a valid reason why other than he felt it was polluting an indoor pool and was unnecessary. I did tell him that I installed a UV Sanitizer and told him that others had recommended that I put at least 20-30ppm of CYA in the pool that it would help to keep the chlorine levels a bit more stable, but again he did not offer up a reason as to why he still did not recommend it. Is there a water or air quality issue with the addition of CYA in an indoor pool? I get that the more you add the higher you are going to need your chlorine levels to be to effectively sanitize. Off the top of my head I thought is was somewhere between 7.5 and 10x FC to CYA? I am definitely limited by the state in that I can't have my chlorine about 3ppm though, but we are constantly at or over that amount because of the problems in the past of letting it get low and when the bromine would begin to accumulate too much DMH we had problems keeping the levels under the limit and keeping the pool clear as well.

Any recommendation on an ORP system?
 
20-30ppm CYA would be compatible with state regulations for an FC of 3ppm or less. And at that level it shouldn't mess up an ORP probe.

Very good reason to add it - bather comfort! At 3ppm FC and 30ppm CYA, the concentration of hypochlorous acid is high enough to kill bacteria, algae etc but almost undetectable in terms of bather comfort. With 3ppm FC and zero CYA, your hypochlorous acid concentration is some 15X high in comparison. That's harsh on skin, eyes, bathing suits, etc.

Also, adding CYA reduces the formation of nasty nitrogen trichloride (bad pool smell) in favor of monochloramine which is much less harmful (monochloramine is used in drinking water sanitation).

If you can add CYA, then do it. Your bathers will be very happy.
 
I'm not sure how much CO2 you'd be using, but I have a pair of cylinders, and keeping them filled is pretty easy. It's just a swap. I take the empty cylinder in and they replace it with a filled cylinder. It's a little heavy, but not so much that it's a big pain to load it.

You may be able to find a local gas or welding company that will deliver cylinders on call pretty reasonably.
 
Thanks for the info, that makes a lot of sense. Especially since I have a lot of elderly who use the pool and many of them have various skin sensitivities due to a lot of the medications they take so anything that would bring a bit more comfort would be helpful. I am going to make one last push to find out if it is absolutely not allowed either locally or in the state and if it is I will try to add 30ppm of CYA and keep the FC as close to 3ppm as possible.

Also I am using the next few weeks to see how much chlorine I am going through on a daily basis and also how much acid I need to add to keep the pH in check. As of now we are adding about a gallon every night to keep FC above the 2-3ppm as it is dropping about 2ppm throughout the day and have had to add a little bit of acid about 1-2x week to keep the pH below 7.6.
 
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