Raising ORP value

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dvcavall

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May 14, 2012
13
Hello everyone. I am new to the forum, but have found it very informative already. I'll try to do an intro at another time. Here is my haunting question. What do I need to do to increase my ORP value? Depending on whether you subscribe to the saturation index range of -0.5 - +0.5, or if you prefer the -0.3 - +0.3 range, my pool water currently may or may not be balanced as my calc was the former. However, my ORP meter only shows 412mv which is far less than the 650mv said to be a minimum figure for good sanitation? The only thing I can think of is that my CYA needs to be lowered. My readings today were as follows:

FC: 2.27
TC: 2.31
TA: 93ppm
PH: 7.4
CH: 356
CYA: 37ppm

I also had a Phos level of 150, and TDS of 1200. Any thoughts? Oh yes. I purchased some ORP calibration fluid at 400mv. The meter read just over 400mv before I calibrated it to read 400mv on the nose. Granted, it is only a relatively inexpensive meter (HM ORP-200), but I believe it is reading correctly.

Dave
 
ORP readings are not a reliable indicator of water sanitation. There are several factors that change the ORP reading that have nothing to do with sanitation.

Your FC level is too low. With CYA around 40 you should be keeping FC between 3 and 5, and never below 3.

Also, it is misleading to list test results with that level of apparent precision. None of the water tests are that precise. It is more appropriate to round to the nearest multiple of 10 (for most of them) or 0.1 (at best) for PH, FC & CC.
 
Thank you for the reply. I am using a Lamotte 2056 colorimeter digital kit, and those are the readings it gave, so the readings I gave. I am also using a mineral sanitizer (Zodiac Nature Express 2) which indicates that a much lower chlorine level can be used, but I agree I need to increase my dosage. I had been running a Jandy salt system, but it died this winter and I have not found a price I can afford to replace it, so I am adding chlorine by hand, and need to track things better.

I think the most frustrating thing about pool care is that everyone has a different opinion about everything, and no one set of parameters are accepted as the ideal. Below are what Lamotte calls the IDEAL RANGES. Clearly your lowest range for FCL is their highest.

As far as ORP, is the addition of CL all you would suggest? Is 650mv reasonable to strive for?

Test Factor Pools PPM
Free Chlorine (FCl) 1.0 - 3.0
Total Chlorine (TCl) < 0.5 above FCl
Total Alkalinity (TA) 80 - 120* or 100 - 150**
pH 7.2 - 7.8
Total Hardness 200 - 500

*Use a 80-120 alkalinity range for pools/spas using high pH sanitizers such as sodium hypochlorite
[liquid bleach] or calcium hypochlorite. Use this range if Total Hardness is >300.
** A higher (100-150) alkalinity range is best for pools/spas using low pH sanitizers such as stabilized
forms called dichlor or trichlor as well as bromine.
 
As I said, ORP readings are not an appropriate indicator of sanitation and thus aiming for any particular ORP level is meaningless. Target a specific FC level based on your CYA level.

The LaMotte ranges make a number of unstated assumptions. For example they assume that your CYA level is very low. Their FC recommendations are not valid when CYA is higher than 10 or 15. Likewise they don't take the pool surface into account when setting their hardness target.
 
I'm just jumping into the deep end of Pool chemistry after 6 years of pool ownership, so I am reading studies and trying to make sense of it all.

I have read that world heath orgs have incorporated ORP standards into pool and drinking water sanitation, and the World Health organization established a threshold of 650mv for instantaneous bacteria and viral inactivation. Other studies seem to indicate that ORP, and not FC,L most accurately predict the killing rate of undesireable organisms like E. Coli. PH and CYA have a substancial impact on the effectiveness of the free chlorine to oxidize, and there are numerous studies and charts showing the relationship.

What it all means to the average pool owner as opposed to the high usage public pool AFO I am not certain, and suspect not much as the pool usage (at least at my home) is generally very low.

As they say, a little knowledge can be dangerous, so I am trying my best to learn what I can. I am planning to take the CPO class and the LA County certificate exam in a few months. Clearly I still have a bit of learning to do.

Thanks again...
 
CYA in pool water interfers with the ORP relationship to sanatizer (chlorine). The more CYA is present, the less ORP changes with changes in chlorine levels. Because of this CYA levels above about 20 ppm make ORP useless for chlorine control. This fact is not mentioned by ORP instrument manufacturers. This effect is so pronounced that at a CYA level of 80 ppm (SWCG) ORP will not change at all with chlorine level!
 
Welcome to tfp, dvcavall :wave:

dvcavall said:
I am planning to take the CPO class and the LA County certificate exam in a few months.
Click to expand...
Then you may (or may not) want to read this: http://www.troublefreepool.com/certified-pool-operator-cpo-training-what-is-not-taught-t18432.html

Also take a look at this post (I noticed you have a nature2): http://www.troublefreepool.com/alternative-sanitizers-and-chemical-free-pools-the-truth-t3025.html I believe the Nature 2 express is a "mineral system".
 
Take a look at this post for way more information on ORP.

Most of the early studies that support ORP as the primary measure, and essentially all of the popularization of those studies, were funded by companies selling ORP controllers. Many of the more recent studies have invalidated significant portions of their results.
 
Also see the "Chlorine/CYA Relationship" section in Certified Pool Operator training -- What is not taught thread and its links to scientific peer-reviewed papers including some on ORP. It is the active chlorine (hypochlorous acid) level that matters. ORP is just a proxy for that, but can be fooled by oxidizers that are not sanitizers. Also, oxidation potential is not the same as oxidation rates. Technically speaking, oxygen in the air should be destroying your body (oxidizing organics) right now, but fortunately the reaction rate for that is very slow even though the thermodynamics of it (which is what ORP measures) says it is possible.
 

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Even if you can get a minimally consistent correlation of FC to ORP values (e.g. >700 = >3 FC), usually you can get a more accurate control of your FC - just by controlling how often the SWG runs. To the extent the ORP values are useful, it is more to state when the SWG should NOT be running than when it should.

I would recommend the hybrid approach.

I have an intellichem, and most days an ORP reading of 700 means a reasonablly good FC....however various factors during the day can move the orp sensor up to 150 points in either direction (safety cover opening is the biggest, UV rays getting through cover between noon-2pm is also a biggie). Running the SWG for an extended period can also dampen ORP readings. Consequently, the best setup at the moment is to have the intellichem manually run the SWG in a continuous 8 minute on, 11 minute off cycle except when ORP values are >800, at which point the SWG is disabled until the ORP falls under 800. This usually gives me a consistent FC between 4-6 when cya is between 30-40, and automatically disables the SWG when I'm shocking or if FC climbs too high. A persistent ORP value in the low 600's throughout a week can be an indicator that the SWG schedule should be increased.
 
Thanks MattM, It sounds as though you are able to indicate and use ORP readings as part of your pool management, even though you have CYA levels in the 30-40 range? A previous post stated that..."CYA levels above about 20 ppm make ORP useless for chlorine control." If I read your post correctly, it appears that hasn't been your experience?
 
dschlic1 posted the 20 number, which I disagree with. ORP can be used for chlorine feed automation even when CYA is up to perhaps 50 (though there is no hard upper limit, it is already getting problematic with CYA around 50). And even that is something you would only do in a commercial pool, recalibrating your ORP target frequently to your FC reading. My point was that you can't use ORP as your reference number. You calibrate your ORP target based on FC drop test results (something which needs to be done frequently).
 
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