General question on accuracy of drop tests vs other tests

[PoolingInKC]

Starting out by saying that I have the full TF-100 test kit plus the K-1766 Sodium Chloride test kit and I use them religiously and have for 5 years. Recently my IC-60 stopped reading the salt content of the water correctly (shutting it down) and in the interim, trying to prove to the pool service company that there was, indeed, a reading error, I took a sample of my water in and had it tested on a machine. The IC-60 unit was bad and has been replaced under warranty - it was literally 6 months old!!

Anyway, the readout I got back from the pool water test was off A LOT in a couple of areas and I wanted to inquire as to whether this is the norm. It seems that being off +/- 10% would be OK but these numbers are ridiculously incorrect. Here is what I came up with using my TF-100:

Salt: 3200 (this is low, it just rained, after it evaps I will add salt if I need to)
FC 8
CC 0
PH 7.5
CYA 70/80 (small vial comparator @ 80, large TFTestkits vial @ 70)
TA 60 (bringing this up to 75, added soda this morning)
CH 375

Here is what the pool water test said:
Salt: 3200
FC 9
CC 0
PH 7.5
CYA 110
TA 35
CH 125

So the glaring difference are in the CYA, TA and CH readings. Have you guys ever seen something that far off on a water test? I follow the instructions implicitly on the drop tests including wiping the tip of the bottle between drops of R-0009 on the TA test. I am stumped as to why the pool water test is so far off....I mean, not even CLOSE. There is no way my CYA is 110 based on the tube test. TA took 6 drops to change colors = 60. CH drop test took 15 drops likewise x 25 = 375.

Thoughts and musings?

Thanks!

 

[rumcglot]

In way of musings... Don't you find it compelling that you can describe how you performed the tests: "I follow the instructions implicitly on the drop tests including wiping the tip of the bottle between drops of R-0009 on the TA test."? But you can't say anything about how the pool water test (pool store?) performed the test. It was a machine, I guess? When was it last calibrated? cleaned? When was the operator trained?

That's the difference. You know how you did your test.

I'm surprised you didn't say anything about the CC. That seems really high. Are you addressing it?

 

[PoolingInKC]

Yes, it was a machine and have no idea when it was cleaned or calibrated....good points!!

My bad, the CC was 0.......CC, not the TC!!

In other words, to clarify there was no change in color when the 5 drops of R-0003 were added.

Fixed.

 

[jark87]

The pool store near me must have the same machine, as I have the some of the same areas of discrepancies: TA and CH. Store always has them much lower than my tests. On the occasional trip to the store, I usual take a water sample, just to see what their results are and have come to expect those variances.

 

[lawjohn]

I am bringing my pool up after a new resurfacing the pool....Leslie's gave a TA that was way off what it was getting with my TFP chemicals...I called Taylor which is the company that distributes the chemicals and also the test kits to businesses .....the person I talked to told myself to trust my measurements and not Leslie's as they are there to sell me chemicals. I brought my TA up to 100 ppm using my test as instructed and no cloudiness has occurred from too much buffering......I also recall on this forum many years ago the same advice........hope this helps, John

 

[tim5055]

I'll answer part of it....

Most pool stores give and adjusted TA as they deduct for the CYA in the water. Their TA reading will always be lower for TA.

Also, most people keep their TA artificially high. Most of us around here find TA of 50 - 60 is perfect.

 

[Orion7319]

I'll answer part of it....

Most pool stores give and adjusted TA as they deduct for the CYA in the water. Their TA reading will always be lower for TA.

Also, most people keep their TA artificially high. Most of us around here find TA of 50 - 60 is perfect.

My salt cell says to keep my TA between 80-120, the pool store tells me to keep it that high, most sites on the internet say the same thing so that’s where I kept mine and I was adding acid every other day to bring the PH down. A few weeks ago, someone here suggested I lowered my TA down to 50-60 to keep from having to lower my PH all the time. I let my TA drift down to 60 and my PH seems to have leveled off at around 7.6 and I haven’t added any acid for 10 days now, so this certainly seems to work for salt pools!

 

[tim5055]

My salt cell says to keep my TA between 80-120, the pool store tells me to keep it that high, most sites on the internet say the same thing so that’s where I kept mine and I was adding acid every other day to bring the PH down. A few weeks ago, someone here suggested I lowered my TA down to 50-60 to keep from having to lower my PH all the time. I let my TA drift down to 60 and my PH seems to have leveled off at around 7.6 and I haven’t added any acid for 10 days now, so this certainly seems to work for salt pools!

It works for most pools. They will usually find their happy place and settle in. My pool was in Lexington, SC and it liked 50...

 

[Orion7319]

It works for most pools. They will usually find their happy place and settle in. My pool was in Lexington, SC and it liked 50...

Yes I just quit fighting the TA to see what would happen. It seems to like 60. Mines in Rock Hill. What were your water temps this time of year? Mines been hovering around 90 and I think that’s perfect..

 

[tim5055]

Mine was usually 85 - 90 most of the summer

 

[Orion7319]

Mine was usually 85 - 90 most of the summer

OK, thanks! This is our first full year in this house with this pool and I hope it doesn’t get into the 100’s.

 

[jseyfert3]

Also, most people keep their TA artificially high. Most of us around here find TA of 50 - 60 is perfect.

I mean it's perfect, right? If left alone, the TA will drop until it's in equilibrium and acid used goes way down...but if the pool store tells you to keep it at 100 then you have pH rise so they sell you acid to lower that which lowers TA, so they sell you TA increaser, which speeds up pH rise so they can sell you more acid, which...

I mean, it's perfect for them, not perfect for the frustrated pool user. Who eventually gives up on pools or finds their way here, both which result in the loss of a customer for the pool store. So actually, maybe it's not so great for the pool store in the long run?

 

[PoolingInKC]

Great information on the TA issue.
"If left alone, the TA will drop until it's in equilibrium and acid used goes way down."
This actually 'splained it the best.
Thanks!