ColorQ vs. TF-100 (accuracy?)

[Kermiter]

I've been using the digital ColorQ Pro-7 pool tester for about a month (after getting a new PebbleTec surface). Based partly on this thread, I also purchased a TF-100 to compare the two and because I have heard it's more accurate, especially for CYA (stabilizer). For those who don't know, the ColorQ is an optical color reader (my non-technical description). For each test, you add drops (or crush a tablet for CYA), place the vial in the device, and press a button to get your digital reading.

I am not an expert. I am new to this forum and to managing my own pool. I'm posting this here just for conversation.

Here are the results of my first test:

June 9, 2011 - 3:00pm EDT (water temp: 83F)
--------------------------
.......... ColorQ .......... TF-100
FC ........ 2.32 ........ 4.0
TC ........ 2.42 (CC 0.1) ........ (4.0) CC 0.0
PH ........ 7.4 .......... 7.8
TA ......... 81 .......... 80
CH ........ 227 ........ 450
CY ........ 47 .......... 38
CSI ....... -0.25 ...... 0.39

(Is there any way to make HTML tables in phpBB? Also the List= function doesn't appear to be working.)

My initial observations, given this is just a single test:

• 
  1 -- FC is significantly different. [EDIT]The 4.0 reading above is from the Chlorine Drop Test where you count the number of drops as the water color changes. I also used the "OT Test" that also comes with the TF-100, where you match against the colors alongside the vial. That result, as close as I can tell, was between 3 and 5.[/EDIT] I'm not colorblind but I do have a hard time with the color-matching tests. The FC scale on the TF-100 is 0.5, 1, 2, 3, 5 and it certainly wasn't showing below 3. Today I'm going to be conservative and go with the ColorQ result (it's time to add chlorine anyway). The last time I added chlorine was two packets of Lithium Hypochlorite on Monday night (June 6) taking it to FC 5.23. Prior to that, I took the pH from 7.7 to 7.1 during the day (overshot 7.2 a bit). My last five FC measurements with the ColorQ have been: 5.17, 4.26, 3.92, 3.18, 2.32. Yes, I know I'm currently a little low on FC for my CYA level; that will be fixed tonight.
  
  2 -- If the ColorQ is correct on TC, I presume CC is close enough to 0 to call the tests a match.... (?)
  
  3 -- PH, again, could have something to do with my ability to color match. It [EDIT](the TF-100)[/EDIT] seemed to show at or close to 7.8, but it was certainly above 7.5. [EDIT]Its scale is 6.8, 7.2, 7.5, 7.8, and 8.2[/EDIT]
  
  4 -- Calcium Hardness has me concerned because it's such a discrepancy. On the TF-100, I may be putting in too many of the third set of drops (R-0012). Pool store tests repeatedly show CH between 170-260 (from multiple different stores), in range of what I'm seeing on the ColorQ. (They also repeatedly show 0 copper.) In my observation, during the CH test, the color goes from Red (more like pink) to Purple and then to a seemingly more "blue-ish" color. It took me 45 drops until I was comfortable calling it "blue-ish" but not nearly as many (only about 25) to be comfortable calling it Purple. Am I over-analyzing this one?
  
  (Another observation I have on the CH test is that the reagent requiring 20 initial drops (the R-0010) also comes in the smallest bottle size. Hmmf.)
  
  5 -- Stabilizer. With the ColorQ, you crush a CYA tablet into the vial of pool water and wait 2 minutes before measuring CYA level. With the TF-100 you mix a liquid CYA reagent with pool water, wait 30 seconds, and pour it into a narrow vial. The vial has a black dot on the bottom, and you stop pouring when you can no longer see the dot. You then read your CYA measurement in ppm on the side of the vial. My reading was 47 ColorQ vs 38 TF-100. I probably added a few more drops to the vial than I needed, but my mind was telling me, "Hey I think I still can see a hint of that dot poking through if I squint hard and concentrate." :tongue: I'll give this one a few more tries before worrying too much.

Obviously, I would prefer seeing closer numbers between the ColorQ and TF-100. TA was the only one that was right on. So which one is more accurate? I'll continue testing with both kits and seeing how the numbers compare. (And, yes, by now my wife is starting to wonder if I'm becoming a little obsessed...)

Another note about my pool surface: It's one month new PebbleTec and, aside from a packet or two of Cal-Hypo, I haven't added any calcium chloride since filling. I've been a bit nervous about my "low" CH numbers since the pool opened, because I didn't want to be leaching calcium out of the new surface. CH has mostly read below 180, but the past five days has been 182, 187, 217, 221, and 227 (all with the ColorQ). With the 450ppm result from the TF-100, now I don't know what to think. But my water is crystal clear and I'm not freaking out.

 

[Kermiter]

Sorry, I was a bit ambiguous when describing my TF-100 chlorine test results.

FC showed 4.0ppm using the TF-100 Chlorine Drop Test.

It was between 3 and 5 (my best guess) using the color-match test kit that is also included with the TF-100.


There's pre-Submit proofreading, and then there's post-Submit proofreading.

 

[JasonLion]

I believe that the TF100 is more likely to be correct, especially if it is new this season. There are several ways that one or another of the tests in the TF100 could go wrong, but being nearly consistently off by that much on a number of different tests makes me suspect the ColorQ. It is far easier for the ColorQ to be consistently off, because all of the tests depend on the same electronics. While the TF100 can be off on one or another test in some situations, they all use different reagents and the odds of most of them failing in the same direction at the same time are microscopic.

 

[duraleigh]

(Another observation I have on the CH test is that the reagent requiring 20 initial drops (the R-0010) also comes in the smallest bottle size. Hmmf.)

Done on purpose. We have been able to keep the same price of the TF-100 for fours years by tweaking our costs. The R-0010 is one of the more expensive reagents.

The 15ml bottle allows enough reagent to perform about 18 CH tests. Since CH is a very stable item, most folks have no interest in testing CH more than 2-3 times yearly.....so that works out to about a six year supply.....far longer than I would like to see folks continue to use the reagent.

 

[loop_pea]

If you have trouble with colours, then I guess it's harder to do colour matching, and that could throw up some errors even though the test itself is working as it should.

I am good with colours but with the phenol red test reagent I think it's hard to tell the difference visually for anything over 7.6.

 

[Kermiter]

Well, it could be user-error, too. I'm sure I'll get better at it with practice. I'm not biased against either test. I find the ColorQ easier to use, but my utmost desire is accuracy. I don't have enough experience to draw my own conclusion right now.

Can the TF-100 experts let me know if I'm goofing up on the CH test? See #4 in my original post.

Thanks!

 

[JasonLion]

Purple during the CH test is called a fading end point, and often results in invalid results. Do the test again, but this time add five drops of R-0012 before adding any R-0010 or R-0011L. Remember to count the initial five drops in the total. In extreme cases, a fading endpoint may occur even when adding five drops of R-0012 at the start. If that happens, mix pool water with an equal quantity of distilled water, test that, and then multiply the result by two.

 

[XsAllOverIt]

Here are results from my pool from Sunday.

ColorQ TFT100
fCL 3.91 4.5
tCL 3.91 4.5
pH 7.4 7.5
ALY 71 80
CH 179 300
CYA 60 55
Salt 3600

My ColorQ has been pretty consistent from the beginning that CH is always lower. Otherwise pretty consistent.