Testing result I do not understand....

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E

eqbob

0
Jul 25, 2012
436
Central Texas
Basically, CYA tested *higher* after a night of very significant rain (several inches) Other than salt, no other parameters were significantly changed. Salt decreased several hundred ppm (3300 to 2650) and CH went down from 280 to 250. Those changes all make sense to me which is why I tested this morning after the rains were over.

What doesn't make sense is CYA tested higher by 15ppm. The inky explanation I can think of for that is operator error, although I've did the test the same way as always (it's subjective but not difficult to perform).

Any thoughts?
 
CYA cannot go up unless you add more....it does not occur naturally.

Margin of error on the test is plus or minus 10 ppm.

Just curious why you performed CYA tests so close together...........3-4 times per swim season is generally often enough.
 
duraleigh said:
CYA cannot go up unless you add more....it does not occur naturally.

Margin of error on the test is plus or minus 10 ppm.

Just curious why you performed CYA tests so close together...........3-4 times per swim season is generally often enough.
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Just habit of doing all the tests, all the time. Learning, seeing what changes, what doesn't, etc. Generally figuring out the pool ....

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PAGirl said:
Was it cloudier than it had been the last time you did the test? Brighter lighting?
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The pool water was/is the same, but the lighting conditions were certainly different. Overcast, no sun.
 
The cya is operator error. The other tests results seem off as well. That would take a significant water change/dilution to lower salt by 650ppm. According to pool math that is a 20% water change. How are you testing salt? Strips or Taylor K1766? The 1766 that I use is pretty much impossible to read wrong. The strips, not so.


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The CYA test seems to cause newbies like me the most problem in getting a reasonably accurate measurement. I've had +/20ppm depending on light conditions and the person reading it. Peering over the top of the Taylor tube, I've even confused the shadow of my head with the black dot!!

Been thinking about getting a CYA standard 50ppm sample, then putting the test tube on top of my AC plugged-in smartphone with a paint app that can vary the 'whiteness' of a full screen background to a known RGB in a dark room, and calibrating the RGB against the sample. Although I haven't got the sample yet, I do this already on my pool water and get consistent readings each time using the same 'white' background, assuming I'm not losing CYA over the last 3 weeks (haven't needed to backwash, drain & fill, or losing much to splash out)

Any thoughts on this method?

Mike
 
Turbidity can also effect your readings, but I would think you would notice if the water was cloudy enough to make a difference in the reading.
 
bdex said:
The cya is operator error. The other tests results seem off as well. That would take a significant water change/dilution to lower salt by 650ppm. According to pool math that is a 20% water change. How are you testing salt? Strips or Taylor K1766? The 1766 that I use is pretty much impossible to read wrong. The strips, not so.


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I've been reading it from my SWCG. Even if it is off, it's the same device, so one would theorize consistently making the same error. Even if it isn't reading it entirely correct it's acting based on what it reads, so I have to make it happy to operate properly.

I had thought about a good electronic tester for salt to reduce the error but those little electronic puppies cost a few hundred bucks and they seem to be horribly prone to calibration errors and disliked by postings here. I do not know about a Taylor K1766 and will look that up.

We had torrential downpours for several hours and got several inches of rain. This was not a normal, insignificant rain event of a shower for an hour. Three days later, I still have standing water in the backyard and we're squishy and wet most everywhere.

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chiefwej said:
Turbidity can also effect your readings, but I would think you would notice if the water was cloudy enough to make a difference in the reading.
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There's been no visible change in the cloudiness of the water. Can certainly understand where that would change the reading and will be alert for that in the future.
 

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I feel your pain on the SWG having to be happy. They have a pretty large range that they will operate in and are by and large not that accurate. I would pick up that Taylor kit and then you should be able to recalibrate your cell based on that reading. That is what I did with my compupool and it has been about dead on ever since.
The error in its number is likely because it is drawing water off of the skimmer (top) of the water. Which is much more heavily concentrated with rain than the bottom of the water or even more so deep end.

Give the pump time to mix it up or swim in it and I bet it rebounds.


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bdex said:
I feel your pain on the SWG having to be happy. They have a pretty large range that they will operate in and are by and large not that accurate. I would pick up that Taylor kit and then you should be able to recalibrate your cell based on that reading. That is what I did with my compupool and it has been about dead on ever since.
The error in its number is likely because it is drawing water off of the skimmer (top) of the water. Which is much more heavily concentrated with rain than the bottom of the water or even more so deep end.

Give the pump time to mix it up or swim in it and I bet it rebounds.


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Found K-1766 on amazon and already ordered it in on prime. Wouldn't the water draw be both from main drains and skimmers?

I don't know of any way to recalibrate the salt cell. I asked Pentair about that when they visited my pool a few weeks ago and they indicated there was no way to recalibrate an InteliChlor. I'm sure there is within their factory production line, but interpreted that as not out in the field, being used.
 
Looks like pentair changed that with the new ones. We had an older version and it was a breeze if you knew your salt level and how to do it. That sucks. And yes, some water would come from main drains and some from skimmer, but 50% rainwater and 50% 3200ppm saltwater will drag the number down. You may have to add a little salt, but if I had 20% refill rate rain my pool would overflow in a snap.

Check NACL with the 1766 and report back.

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Will do.

Also, wanted to relate, that the salt cell, after 1 bag added, increased it's reading from 2650 to 3050, an increase of 400 ppm.

Since one bag is stated to raise 10K gallons 500 ppm (i.e. 6 bags for 3000 ppm), one bag into 12K gallons should raise it slightly more than 400.

Which is exactly the behavior I saw.
 
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