Accuracy of Testing Strips

Cultcab

Active member
Oct 23, 2016
42
Roseville, CA
I am trying to see if I can simplify my life by switching to testing strips to cover some of the tests that I do on our pool. I purchased a batch of the AquaChek 7-way test strips and I compared it today to the results I got with my Taylor FAS-DPD kit:
CL: 14 ppm Taylor vs 10 ppm AquaCheck
FreeCl: 0 ppm vs 10 ppm
pH: 7.8 vs 7.2
Alk: 80 vs 40
TH: 150 vs 500
CYA: 80 vs 30 - 50

I was hoping that at least 2 or 3 of the tests would have comparable results, but none of them really matched closely.

Another oddity was that I have never registered a FreeCL reading using my Taylor kit (which also seemed weird to me) and the test strips showed a reading of 10 ppm.

I am planning on repeating the comparison a couple more times, but I wanted to hear if anyone else has had some success using the test strips.
 

jmastron

LifeTime Supporter
Jul 21, 2014
344
Sacramento, CA
I am almost certain that your test strips are showing Free Chlorine (FC) and Total Chlorine (TC). Total Chlorine is by itself a pretty useless number; subtracting TC-FC gives you "Combined Chlorine" which you want to be less than 1ppm. Your test strips are showing FC=10 and CC=0 (FC-TC) which is good.

The steps of the Taylor FAS-DPD test give Free Chlorine and then Combined Chlorine directly. You're showing FC=14 and CC=0 there, so the only discrepancy is the Free Chlorine.

The Taylor test reports Calcium Hardness, not "Total Hardness" if that's what the strips show; I don't know

As others have stated, the drop tests are considered more accurate; I personally wouldn't bother with the strips. Once you get a feel for the pool, you don't really need to run all the tests that often, especially here in CA where we don't have much rain during the swim season affecting the chemistry. I only test TA, CH, and CYA every couple weeks or less often during the summer, even less in the winter; they don't change much.

FC and pH are the more frequent tests; even those I only run every 2-3 days in the summer (with an SWCG where I have pretty predictable changes; I ran the FC test every day before adding when I was pouring liquid chlorine). I usually don't bother with the CC part of the FAS-DPD test as long as I know the FC has never gone before the minimum.
 

Newdude

Gold Supporter
TFP Guide
Jun 16, 2019
11,561
NY
Worse than their inaccuracy is the ever changing colors. Wait 15 more seconds and they change. Did you spot it at the exact moment it was closest to correct ? Or were your Mississippi's too quick/slow ?

Also. Let's look at their own say so for CYA. 10, 20-50, 50-100 and 100-200 is the perfect example for how little they actually tell you. Then you dose LC/FC per a vague guess ? That pool is gonna be Shrek green in no time.
 

Donldson

TFP Expert
LifeTime Supporter
Jun 12, 2009
5,164
NW Ohio
I know this thread is about test strips (junk, throw them out) but if you're consistently reading a high Total Chlorine level but never able to get any Free Chlorine to show up on the test, then either there's a testing error or a really bad problem with your water chemistry. That should take priority over further experimenting to find just how worthless test strips are (very worthless, throw them out).
 
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jmastron

LifeTime Supporter
Jul 21, 2014
344
Sacramento, CA
I know this thread is about test strips (junk, throw them out) but if you're consistently reading a high Total Chlorine level but never able to get any Free Chlorine to show up on the test, then either there's a testing error or a really bad problem with your water chemistry. That should take priority over further experimenting to find just how worthless test strips are (very worthless, throw them out).

I was assuming when OP reported "CL 10" and "FreeCl 0" from the Taylor test, they must have meant "Free Chlorine 10" and "Combined Chlorine 0", because that's what the drop test measures (vs the strips, which show TC/FC). And FC 10 is closer to the FC measured by the strips. But I agree, if that's not the case and FC is really 0 that's the first priority to resolve.
 
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Cultcab

Active member
Oct 23, 2016
42
Roseville, CA
Thank you all for your input on the test strips.

I knew that their reliability was questionable, but I was hoping that they would at least be within the ballpark on a couple of the test. I've already deposited into the garbage can, and I’ll stick with the Taylor method since it’s been working well for me for years.

I inadvertently switched the chlorine readings in my original post. That should’ve read that the Free CL reading was 14 ppm and the combined CL was 0 ppm.

I meant to say that I have never registered a combined chlorine reading using my Taylor kit.

Is this abnormal?
 

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