Me vs. The Pool Guy

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michaelrbanks

michaelrbanks

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LifeTime Supporter
Sep 19, 2014
92
Cibolo, TX
I had an interesting opportunity yesterday. The pool builder sent out a tech for routine service under the first year protection plan & I got to watch him test my water. He was packing a Taylor K-2006 & knew how to use it. All the parameters for pH, TA and CYA matched mine perfectly, but the FC was off. We both used the DPD method of testing FC.

At 6:00 a.m. that morning, I tested and added enough bleach to bring it up to 5.5 PPM.
Pool Guy showed up and tested around 3:00 p.m. after the pool baked in the sun, so I expected some loss. He got 3.0 PPM.
I did not do anything after he left until 6:00 a.m. today. When I tested this morning, I got 4.0 PPM

So where did the extra chlorine come from? :confused:

Some notable differences between how we tested: I test early in the morning at the deep end, pulling water from probably 6-8" below the surface. Pool Guy tested in the blistering afternoon sun in the shallow end. I did not notice how deep he sampled.

Could there really be a 1 PPM difference within my pool, based on sample location?
 
Yes, those difference can/do make a differences in your results. Some people don't think too much about it for normal everyday testing of FC, but you can best when it comes to an OCLT where 1ppm means the difference between a SLAM or not, you test like a robot and standardize everything you do. At least you are experienced and now.
 
if the water's not circulating, the water at the top would have a lower FC due to higher sun UV exposure. And, if your water isn't circulating, that's probably the better reading to have, as it shows where the weak point in your water might be where algae could grow. If you're close to your minimum, part of your pool might be at risk for algae by the end of the day.
 
I grab my test water from the exact same spot each time.

I dunk my bottle in up to my elbow. I don't think I'm growing any more (46 :) ) so that should be consistent.

As long as you do it the same, you can just rely on your own test results and any changes should be accurate even if your actual numbers are off a bit.
 
BuckeyeChris said:
if your water isn't circulating, that's probably the better reading to have, as it shows where the weak point in your water might be where algae could grow.
Click to expand...

This is an interesting observation - I may have to take a few samples around my pool & find my weak point. That would then be my control location.

Agent99 said:
As long as you do it the same, you can just rely on your own test results and any changes should be accurate
Click to expand...

I wholeheartedly agree! If you're wrong, but consistently wrong, that's so much better than being inconsistent!
 
Yeah, if you are a person with lots of free time, you could find the batch of water in your pool that always seems to have the lowest FC and then make sure that's above the minimum. But really, just adjust your filter times and stay 1 PPM above the minimum and you'll be fine.
 
When I was trying to figure out my pool this spring in my first year of ownership, I was having trouble with the DPD test- I was getting no FC reading, but if you waited a few minutes, the sample would turn pink, which I mistakenly thought was FC. I realized my mistake when I pulled a sample of water (from the same place I always do) and the sample turned deep pink with the addition of the DPD powder (it had been a little while since I added bleach). So, I somehow tapped into a pocket of FC that hadn't been mixed in, as I could not repeat the deep pink color in the 1-2 tests I did immediately after....
 
One thing that you need to correct is the depth of the water sample you use, 6"-8" is not deep enough, make sure you are getting it from 12"-18" deep.

With DPD testing the test has an error accuracy of +-1ppm in the range you are testing. For more accuracy use the FAS/DPD test.
 
What's the thought process on taking a sample directly in front of a return that is about 8'inches deep?
What's the thought process on taking a sample at a less than optimal depth, but if it exceeds minimum, so would the deeper water, yes?
 

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Please remember, TFP is about simplicity, not overthinking the way you manage your pool. If your pump has been running for 30 minutes prior to your test, it should not make a gnat's behind worth of difference where you take your sample. Your water should be blended just fine. Please take a sample from around 12".

If you find you are getting significantly different readings by chasing a "hot spot" or any other technique. The chances are quite good that you need a new pump!!
 
What a coincidence with this thread....just last night, I decided to take my sample from the water coming out of my return after the pump had been running for about an hour.


duraleigh,
you had me with "If your pump has been running for 30 minutes prior to your test, it should not make a gnat's behind worth of difference where you take your sample. Your water should be blended just fine.", which is what I always thought, and then you finish it with "Please take a sample from around 12". I'm confused..
 
This is one reason I split up my pump run time. From 8p to 12a to circulate my newly added bleach, then from 8a -12p to have some circulation in the sun. The other reason is to spread out the skimming function so debris is on the surface for a shorter period of time.
 
take a sample from around 12".
Click to expand...
Just a "good practice" technique.....I think mostly keeping you from pulling in any surface debris. Truth be told, it just might be irrelevant but it's one of those things that I do without thinking. Actually, my wife says that a good portion of my waking hours are spent that way.:shock::shock:
 
I follow the recommendation from Taylor technologies and sample the water mid-pool, at more than "elbow depth".

It's in the section titled "Work with a water sample that's representative of conditions in the pool as a whole." where they offer several good reasons.


That being said, if I understand what I have been reading correctly, the TFPC recommendations are based on pool problems and measurements reported by TFP users. That must mean that the recommended levels are based on water samples from the deep end, if that's where most TFP users get their samples.

The same would apply to any other popular interpretations, such as how to measure the volume of a sample. I'm using a 10 ml syringe I bought at the pharmacy, so I'm pretty sure I get the right volume but it seems to be too low according to the scale on the TF-100 vial. Assuming most TFP users don't use syringes to measure their water samples, the recommendations would then be based on slightly larger sample volumes ?


Either way, the pool is crystal clear and that's the most important parameter. A nice bonus is that the pool store can go entertain themselves.
 
Sparkle said:
I follow the recommendation from Taylor technologies and sample the water mid-pool, at more than "elbow depth".
Click to expand...

That would imply that you essentially need to get into the pool to do any testing, unless you have some rig that grabs water several feet out, several feet deep.


Sparkle said:
The same would apply to any other popular interpretations, such as how to measure the volume of a sample. I'm using a 10 ml syringe I bought at the pharmacy, so I'm pretty sure I get the right volume but it seems to be too low according to the scale on the TF-100 vial. Assuming most TFP users don't use syringes to measure their water samples, the recommendations would then be based on slightly larger sample volumes ?
Click to expand...

Not sure I understand that question. All the tests are based on a known water sample size, such as 45 ml, 25 ml, or 10ml. As long as you're using the recommended sample size for the test, or following one of the known dilution/multiplication of results procedures, you should be fine.

I use my various vials and the Taylor comparator and fill to the appropriate amount required for the test I'm doing at that time.
 

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