Pool Store tests vs TF100

[richmgreen]

For those of you who have not yet purchased a TF100 please read.

As I am preparing my pool to install a SWG later this week, I thought I would have my water tested for salt level .. to see where I am starting from. I first went and bought the AquaChek white test strips for salt. While at the pool store, they also tested my chemistry. The results I got from the store surprised me ... so I decided to take some water to a pool store 5 miles down the road. Here are the test results between Store 1 .. store 2 and the TF100.

Store 1 Store 2 TF100
FC 3.0 5.0 9.0 (I had shocked a couple of days ago to get rid of CC)
CC 1.1 N/A 0.0 (store 2 doesn't test for cc)
TC 4.1 N/A 9.0
PH 7.3 7.4 7.3
CH 175 350 250
TA 111 120 110
CYA 30 100 50 Wow what a range. (The TF100, although subjective, there was no way it was 100 and no way it was 30)

Salt <1500 420 480 (with Aquachek white strips)

Conclusion, stick with the TF100 and be consistant with your own measures.

Not quite shure if I should add CYA for the salt system .. I guess yes using the TF100 to get me to 75-80

How can they differ so much on CYA and hardness ?

 

[JasonLion]

The CYA test is really easy to get wrong, especially if you are in a hurry. If you don't mix it for long enough you will get a lower than actual reading and if you read it in indoor lighting you will get a high than actual reading. It takes a little more doing to get the CH test wrong, though it isn't really all that difficult. The usual problem is failing to swirl/mix the sample throughly enough.

 

[richmgreen]

based on all these numbers, should I still increase my CYA (I assume ... using the TF100 for reading) for the salt implementation.?

 

[JasonLion]

Yes, you want CYA between 70 and 80, measured with the TF-100, for use with a SWG.

 

[rastoma]

Results from a drop test can be off too if not done correctly. Are you squeezing the reagent bottle when doing the FC/CC test? Or are you letting the droplet come out of the bottle on it's on through gravity?

 

[richmgreen]

Squeezing the bottle slightly. What is the correct way?

 

[richmgreen]

Still trying to get the feel for the CYA test ..... Subjective. Is the black dot completely gone .. kind of see it ......

Still though, the range between kind of see it and completely gone is not usually significant.

 

[duraleigh]

Hi, Rich,

Yes, you want the dot to be completely gone. Stand in outside light with your back to the sun is probably the best light and, if you still see the dot, add a little more.

All these tests are somewhat subjective with the CYA test being the most. Don't overthink it. Do the CYA test multiple times with the same solution and take an average of your results.

So, if you get 40ppm once and then 60ppm once, then I would call the CYA 50ppm. You probably won't get that much difference but it gives you an idea that you can be off by a good bit and your result can still be valid and useful.

 

[DWSPool]

I'm more surprised at how different the FC values are. That would appear to be an easier test to get consistency, especially if the stores are using a drop test, not strips.

I have used a variety of test strip brands over the last 5 years and just started using the TF-100 test kit last month - during this past month, I have often taken 2 readings a day with both the TF-100 test kit (the more accurate drop test) and test strips as long as they lasted. I have found that the test strips are actually not too far off, taking into account their lack of sensitivity. So, for a very quick and dirty measurement to see approximately where the pool quality is, they can be useful. But, with the TF-100 on hand, I doubt if I will buy test strips in the future.

The CYA test results can be a little fuzzy, but as someone else pointed out, the difference in CYA value between "sort of seeing the dot" and totally not seeing it is not that large. I sometimes suffer from an overactive imagination, imagining I see it, when perhaps I really don't. When I put another large squirt "just to be sure", I'm usually surprised at how little it reduced the CYA result.

The drop bottles I have do not yield up drops by gravity; I have to squeeze a little to get them off - sometimes, a drop will hang there, and another comes out and I have to count twice. But, all in all, the tests appear to be quite accurate.
-

 

[JasonLion]

Chlorine almost invariably goes down on the way to the pool store, usually due to UV light striking the sample container. Chlorine can also get used up by contamination in the sample container.