ColorQ7 vs Taylor 2006 CH really off.

[Solrayz]

I have had some doubts about my ColorQ7 results for the past several months, since I purchased it tbh. Particularly with my free chlorine and calcium hardness. I really wish I had read through the plethora of threads warning against this unit before purchasing and wasting $200. Another reason not to simply trust reviews, and Youtube videos. I performed multiple tests of the ColorQ and Taylor (2006 FAS DPD) with the same water sample. Both had consistent results but were comparatively off by several factors.

Final comparative test shown

ColorQ Test
fc 5.3
ph 7.5
ta 60
ch 364
cya 24

Taylor Test
fc 4.5
ph 7.5
ta 70
ch 1000
cya 25

Results show Fc higher by 15%, Ta lower by 17%, CH lower by 175% (compared to Taylor test)

ColorQ compensation factors
Multiply ColorQ results:
Qfc - (Qfc * .15) = Tfc
(Qta * .17) + Qta = Tta
(Qch * 1.75) + Qch = Tch

I enjoy the convenience of using the ColorQ, so I don't want to trash it quite yet. Would it be unwise to use the ColorQ7 with the compensation factors I determined?

On a side note, I know my Ch is high. I will be scheduling RO water replacement at a later date. For the meantime I'm in the process of decreasing my alkalinity further (50-60) and Ph (7.4-7.8) to keep my CSI in check.

 

[Jimrahbe]

Sol,

The ColorQ measures Total Hardness not Calcium Hardness.. Yea, yea, I know they label it CH, but it is not.. I specifically asked LaMotte and they told me it is actually TH..

In some places there is not much difference between TH and CH, but in other places there is..

I use my ColorQ all the time and it works well for me, as I am just looking for a change from the previous reading.. When I need to know for sure what the value is, I always use my TF-100..

As an example.. If I know my ColorQ CH reading is 100 ppm too low, I just add 100 to my ColorQ reading and move on...

Thanks,

Jim R.

 

[HermanTX]

I enjoy the convenience of using the ColorQ, so I don't want to trash it quite yet. Would it be unwise to use the ColorQ7 with the compensation factors I determined?

I would be cautious in determining a set of compensation factors based on 1 test comparison. Since this is a election year, you method is sort of like talking to 1 person to decide who will be forecasted to win in a political race. I would suggest you do a couple of different comparisons over time - when the specific results are different like high FC or low pH to determine if you get similar compensation factors or maybe you will need to average your results to get a workable compensation or correction factor as I would call it.
Personally, I do not believe that you can hit on a accurate correction factor between 2 dissimilar test methods. FWIW.

 

[JoyfulNoise]

It's not so much total hardness versus calcium hardness that's the issue, it's because the ColorQ is an "electronic eye", aka a colorimeter, and colorimetry can be very difficult to get right. If the light source ages, or the (plastic!!) lenses get a little fogged up or the cuvette is dirty, the results can be easily thrown off. Also, LaMotte is using a reagent that changes hue (intensity) relative to concentration, but the chemistry of that color change is not at all linear. Color changes can be "linearized" over small changes in concentration but pool water typically spans a very large range (<50ppm all the way above 1000ppm). To expect a reagent dye to have discernible color difference over such an enormous range is unrealistic. This also applies to their FC measurement because the unit is looking at differences in the shade of pink generated by the DPD indicator. That change in pink intensity is not linear at all and can be easily thrown off.

This is why Taylor uses titration. While seeing the color change from red-violet to light blue for CH measurements can be difficult, the transition exists and can be easily seen under the right conditions. It's not perfect either, but titration is always going to be way more accurate than color comparison.

 

[Solrayz]

Hmm interesting. If LaMotte is actually measuring TH instead of CH that would make sense why it is so high. I just wish the Free Chlorine would be more accurate atleast. Very disappointing.

I know I have metals in the water (magnesium precipitate occurs) and I have fading endpoint while performing my Taylor CH test.

 

[JoyfulNoise]

High magnesium levels can interfere with the Taylor test. Rarely does magnesium precipitate out of solution unless the concentration is very high and/or the pH goes above 10.

Wgat would cause you to have high magnesium levels?

 

[Jimrahbe]

Sol,

My ColorQ is about 5 years old, but I get new reagents and test tubes each year or sooner... My FC test is within 1 ppm of my TF-100... I never let my FC drop to a point where a 1 ppm error is a problem..

Thanks,

Jim R.

 

[Solrayz]

Wgat would cause you to have high magnesium levels?

I have no idea. All I know is that the previous owner was using a PoolRX thingy and the pool use to be chlorinated with SWG. I have since removed the poolrx and the SWG from the equation. I really need to schedule a water change.

 

[JoyfulNoise]

PoolRX adds copper to your water. Copper metal ions will interfere with the CH test on tbe ColorQ as well as the Taylor kit. So if the previous owner used that product, your testing is going to be affected.

If RO is available in your area and not as expensive as draining and refilling, then it would probably be advisable to have that done.