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Thread: Accuracy of Test Strips

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    Accuracy of Test Strips

    I am reading a lot about the inaccuracies of test strips from this forum as well as others but I'm a little skeptical. Are these people marketing these products? I'd like to see proof before I spent money on a more expensive test that is more complicated. Are there any studies out there that prove that these test strips are inaccurate? I Googled it but didn't find anything on it.
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    frustratedpoolmom's Avatar
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    Re: Accuracy of Test Strips

    I can only offer you my first hand experience.

    My strips all read "okay". I used them for 5 years, everything said "normal" and good, even though I started having problems in my pool. Then when I'd have my water tested at the pool store, the results were always off from the strips.

    I started asking questions....anyway to make a VERY long story short, I found TFP, got a $20 6-way test kit from Walmart, tested my numbers myself, found my PH/TA were too low and my CYA was well over 100. The strips always told me my numbers were "ok" and the CYA level was 30-50. Ha....nope. Even the pool store confirmed my CYA level was much higher than the strips read.

    Strips are terribly inaccurate, besides being difficult to interpret. Anyone who has used both strips and a quality kit can tell you that - some brands have better strips than others, but I wouldn't rely on them personally. The only ones I would even recommend is the Aquachek Salt test strips and Borate test strips.

    Now, as for the kits, what do you mean when you say "these people marketing these products"? TFTestkits.net, Taylor Technologies, and Leslie's pools, the only three sellers for the recommended kits, are independent of this website. We aren't affiliated with them and we aren't marketing anything, we're just advocating sound testing techniques.

    If you'd rather stick with strips, that's your perogative, of course.
    Helpful links: Pool School; CYA/Chlorine Chart
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    Re: Accuracy of Test Strips

    Dr Nab,

    You should keep all your posts under one thread so folks can see all your information in one "story".....it makes it much easier to help.

    Now....accuracy of strips (and pool stores).

    In two posts you report CYA of 120, 100 and 70.
    You also report CH as 310 in one post and 240 in another.

    That's not accurate enough for good pool water management.

    Good testing will keep your CH +-10ppm and roughly the same for CYA.

    One of the primary things you will find as you read through the forum is that without accurate testing, you will continue to spend your money at the pool store throwing things at your pool and guessing that your pool will turn out okay.....it usually doesn't.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Re: Accuracy of Test Strips

    Also, test strips do not (cannot) measure Calcium Hardness (CH); they only measure Total Hardness (TH) which includes magnesium in addition to calcium and has nothing to do with calcium carbonate saturation to protect plaster surfaces. Test strips do not generally measure to within 10 ppm for Total Alkalinity (TA) or Cyanuric Acid (CYA). CYA in particular is very important since it will determine the appropriate Free Chlorine (FC) level since CYA significantly affects chlorine's effectiveness. Finally, the chlorine measurement in test strips and even in the drop-based OTO and DPD chlorine tests is only approximate and cannot measure higher chlorine levels (above 5 ppm, usually). Only the FAS-DPD chlorine test will measure to within 0.2 ppm for both Free Chlorine (FC) and Combined Chlorine (CC) and can measure up to 50 ppm.

    By the way, you have to be careful when reading websites. Take a look at this link that seems to imply that the test strip will measure Calcium Hardness, but if you read the bottle itself it says Total Hardness!
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    Re: Accuracy of Test Strips

    not to mention the amount of money saved by buying one of the recommended test kits. I bet if every user were able to add up what they saved by testing their own water and not relying on the pool store, it would add up to the thousands, if not tens of thousands of dollars. I know it saved me from a drain, acid wash and refill which would of cost hundreds of dollars alone due to poor pool store CH testing. not to mention the $42/half gallon algaecide I no longer need because of the chlorine/cya chart and fas-dpd chlorine test in the kit. and my pool store uses a fancy laboratory looking setup with drop tests too...for all the good it didn't do me.
    16x32 21,000 gallon in-ground exposed aggregate, 1.5hp pump, 120 sqft catridge filter, birdcage, solar panels, aquavac tigershark qc robot.

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    Re: Accuracy of Test Strips

    I found that the Aquacheck 7 strips that this house had when I moved in were pretty close to what I later measured with the TFP kit. It was just that the ranges on the strips were not very useful and the judgements assigned to the values were wildly inaccurate.

    Let's start with CYA, which has possible values of 0 "Low", 30-50 "Ideal", 100 "OK", 150 "High", 300 "High". So, I tested something between 100 and 150 which seems to be a bit high, not a problem apparently though. I'll guess it is 120, maybe 135, I dunno.

    On to FC, which has possible values of 0 "Very Low", 0.5 "Low", 1 "Pool OK", 3 "Pool OK and Spa OK", 5 "Spa OK", 10 "High", 20 "Very High". So, my FC on the strips is between 1 and 3. Based on the strips, my pool is OK.

    On to TC, which has possible values of 0, 0.5, 1 "OK", 3 "Ideal", 5 "OK", and 10. My TC is 5, which is OK, it says. (No mention on the bottle of the high value of CC's in my pool at this point, so I just didn't realilze that part.)

    So, I added some more pucks to the in-line chlorinator and keep the FC at 2.0 and wondered why I am seeing that flush of green in the spa each day and having to brush the pool so often.

    Now, based on the TFP kit, not the same day, I actually had CYA of 120, FC of 2.0, TC of 4.0, CC of 2.0 and my target range of FC was 9 to 15. I learn that I need to reduce the CYA to around 40 in order to get my target to 3 to 7. And, by playing around with the Pool Calculator, I notice that in order to get to a point of being able to use the strips "Ideal Range" of 1 to 5 FC for my pool and spa, I'd have to have a CYA of 10 And yet, they tell me that CYA is Ideal at 30-50 and not High until over 150

    But, I do still use the strips from time to time. TC of 3 or 5, or higher or lower is useful to know, at my current CYA of 40. And the CYA of 40 is right in the middle of the 30-50 color spot, so that is an easy check if I don't want to take out the whole kit to test it.

    The other tests, pH, TA, are OK but I can't add acid based on the uncertainty of the range given. Total hardness is useless but I did find somewhere that CH is probably 2/3 of total hardness which is about right for my pool. And, the strips are 30 cents per test, which is a bit pricy.
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

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    Re: Accuracy of Test Strips

    Quote Originally Posted by DrNAB
    I am reading a lot about the inaccuracies of test strips from this forum as well as others but I'm a little skeptical. Are these people marketing these products? I'd like to see proof before I spent money on a more expensive test that is more complicated. Are there any studies out there that prove that these test strips are inaccurate? I Googled it but didn't find anything on it.
    I use test strips, oto, and color q

    I use the insta test 6 strips for their speed, but only to get a general idea of what the levels are.
    I use oto to give a more accurate idea of what the TC is
    and the color q for the most accurate results, although I've had mixed results with the color q's CYA testing
    forgot to mention, I find it best to test water at atleast an elbow's length down, naturally this would be difficult with a test strip which would further degrade its accuracy. So basically is comes down to strips being quicker but liquids (drops) being more accurate.
    -Kevin
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    Re: Accuracy of Test Strips

    Quote Originally Posted by X-PertPool
    I use test strips, oto, and color q
    Kevin, have you ever used an FAS-DPD test?
    Helpful links: Pool School; CYA/Chlorine Chart
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    Re: Accuracy of Test Strips

    Nope, never really had a purpose for it yet. The regular DPD test that comes with the color q seems to be pretty accurate for testing FC as well as TC. What are your feelings on it?
    -Kevin
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    Re: Accuracy of Test Strips

    Thank you all for your advice. I appreciate the time and thought put into the responses.

    Duraleigh, sorry for the confusion with the multiple values from different threads. I had the 3 different CYA values because one was from my test-strip, one from the pool store, and one from my other pool at my rental rental property.

    From the replies I am gathering that there is a time when the strips are a nice quick alternative but other times when you need a more precise measurement that you can only get from the drop tests.

    I plan to buy the Leslie's Pool complete service DPD test kit for $85. It tests for FC, CC, pH, TA, CH, CYA. The reagents come in 2 oz bottles (economy size). Is this a good deal?
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    Re: Accuracy of Test Strips

    not at all. the one from www.tftestkits.net is a much better deal (cheaper and better value). this leslie's kit here doesn't even have the fas-dpd test (the dpd test is not the same as the fas-dpd test). actually it looks like a rebranded taylor k-2005 if I'm not mistaken. you can do what you like, but imo if you're going to spend the money you may as well get the one that has the better chlorine test.
    http://www.lesliespool.com/browse/Home/ ... 00/I/81325
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    Re: Accuracy of Test Strips

    Quote Originally Posted by X-PertPool
    Nope, never really had a purpose for it yet. The regular DPD test that comes with the color q seems to be pretty accurate for testing FC as well as TC. What are your feelings on it?
    You maintain pools, but don't have a 'purpose' for it yet? I guess if you haven't tried it you won't understand where we're coming from.

    You really should try it. Seeing as the accuracy can be .2 for detecting FC and CC, and it can test up to 50ppm, IMHO nothing else even comes close for comparisons sake.
    Helpful links: Pool School; CYA/Chlorine Chart
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    Re: Accuracy of Test Strips

    I asked a similiar question and got a great response on the comparison between the drop tests, strip tests, and pool store tests: water-test-equipment-like-the-pool-stores-use-t15439.html
    The avatar is Spalding from Caddyshack
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    Re: Accuracy of Test Strips

    The ColorQ FC and TC tests are fine if your various levels are within bounds. FC and TC need to be 10 or lower, PH generally in range, and CH not too high. If you go outside those ranges the results are not reliable. CH being out of range can be especially problematic, since the CH test on the ColorQ will tend to read very high CH levels as around 300, so you won't know that CH is actually very high and none of your results are correct.

    Test strip results for PH, FC, TC, and TA suffer from very low precision. TH is not very useful, and CYA readings can frequently be wildly wrong. Test strips can also be way off if they have gotten wet before the reading is taken, and over time humidity in the air will ruin them.
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    Re: Accuracy of Test Strips

    Quote Originally Posted by frustratedpoolmom
    Quote Originally Posted by X-PertPool
    Nope, never really had a purpose for it yet. The regular DPD test that comes with the color q seems to be pretty accurate for testing FC as well as TC. What are your feelings on it?
    You maintain pools, but don't have a 'purpose' for it yet? I guess if you haven't tried it you won't understand where we're coming from.

    You really should try it. Seeing as the accuracy can be .2 for detecting FC and CC, and it can test up to 50ppm, IMHO nothing else even comes close for comparisons sake.

    I'm not saying .2 accuracy isn't cool, I just haven't had the need for such an accurate reading, if it was quicker than the other tests I would probably be using it. Keep in mind how my week goes, I am at the property once a week. Not all these pools have chlorinators so I have to estimate how high to bring the FC [most variable factors are unknown or out of my control such as bather load or weather] to last throughout the entire week. This is also basically the only reason I've used any kind of algaecides or phosphate product. I know they are not really needed but any kind of buffer to help pro-long clear water in a pool that is neglected for 6 days a week helps. It's also the same reason why I use Trichlor at all, they slowly dissolve.
    -Kevin
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    Re: Accuracy of Test Strips

    Quote Originally Posted by JasonLion
    The ColorQ FC and TC tests are fine if your various levels are within bounds. FC and TC need to be 10 or lower, PH generally in range, and CH not too high. If you go outside those ranges the results are not reliable. CH being out of range can be especially problematic, since the CH test on the ColorQ will tend to read very high CH levels as around 300, so you won't know that CH is actually very high and none of your results are correct.

    Test strip results for PH, FC, TC, and TA suffer from very low precision. TH is not very useful, and CYA readings can frequently be wildly wrong. Test strips can also be way off if they have gotten wet before the reading is taken, and over time humidity in the air will ruin them.

    I find the color q's CYA testings to be very unreliable a pool that had 150+ cya level tested at 23 according to the color q.
    -Kevin
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    Re: Accuracy of Test Strips

    Quote Originally Posted by X-PertPool
    I'm not saying .2 accuracy isn't cool, I just haven't had the need for such an accurate reading, if it was quicker than the other tests I would probably be using it.
    It takes me just as long to do the FAS-DPD test as it does the OTO test.
    Helpful links: Pool School; CYA/Chlorine Chart
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    Re: Accuracy of Test Strips

    my mom can make an apple pie faster than your mom.
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    frustratedpoolmom's Avatar
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    Re: Accuracy of Test Strips

    Probably, knowing my mom's cooking ability. Ouch.
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
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