Test Strips Give Different Reading To Oto

[macgd016]

I am confused, I have 3 different makes of test strips and they are all showing FC & TC of 1ppm give or take but my OTO tester shows 4ppm, can this be right?

[waterbear]

I am confused, I have 3 different makes of test strips and they are all showing FC & TC of 1ppm give or take but my OTO tester shows 4ppm, can this be right?

I would trust the OTO over the strips. Be aware that OTO only reads TC. I would suggest you invest in a GOOD test kit (I strongly recommend the Taylor K-2006 but not the K-2005). It will save you a LOT of money in the long haul and you will find how easy water testing really is AND have precise and and accurate results. Strips, while accurate (results are repeatable) are not precise (resolution of measurement is small enough to generate useful information).

I suspect that moisture or age has affected your strips since they are reading low. OTO is basically a 'bulletproof' test. It just doesn't tell you anything more than "is there chlorine present?" It cannot tell you if you have FC or CC so its value is a bit limited since we are interested in FC and CC.

When you do get a good kit and ditch the 'guess strips' keep the OTO test. It is useful as a quick daily test for TC and pH. Do the full set of tests in the big kit weekly untill you know your pool and the do the TA, CH, and CYA tests monthly after that since these readings do not change that much in the majority of pools. If you find they do in your pool then continue to test them weekly.

[macgd016]

Thanks for your rely. If I could get a Taylor kit I would but they are not available in Europe and the postage from the US is prohibitive and slow. As all three sets of strips, from different manufacturers and one set is just opened, are giving the same reading I feel that there is more to this than just inaccurate readings

[footie]

Thanks for your rely. If I could get a Taylor kit I would but they are not available in Europe and the postage from the US is prohibitive and slow. As all three sets of strips, from different manufacturers and one set is just opened, are giving the same reading I feel that there is more to this than just inaccurate readings

I use a tablet system for Chlorine and pH similar to this, only the tablets are a different make, I then use a diluting tube to do my other tests, again with the appropriate tablets. I've been doing this for 8 years now and it works for me. One thing I would suggest is to buy a dosing unit if you don't already own one as they take a lot of the hassle out of maintaining the right balance.

[chem geek]

Another good choice in Europe is the Palintest Pooltester SP 315C which tests everything you need (including CH and CYA) mostly in drop-based tests (using tablets for dyes instead of liquids). However, it uses a DPD chlorine test, but Palintest has a FAS-DPD chlorine test now as well though it may only be for the U.S.

[macgd016]

Another good choice in Europe is the Palintest Pooltester SP 315C which tests everything you need (including CH and CYA) mostly in drop-based tests (using tablets for dyes instead of liquids). However, it uses a DPD chlorine test, but Palintest has a FAS-DPD chlorine test now as well though it may only be for the U.S.

Thanks for both the alternative test kit suggestions, I will give one a try but that will take a few days/weeks, for now I still have this discrepancy between test strips and OTO, currently the test strips show 1ppm FC&TC but the OTO shows 4ppm, I just don't get it

[waterbear]

Another good choice in Europe is the Palintest Pooltester SP 315C which tests everything you need (including CH and CYA) mostly in drop-based tests (using tablets for dyes instead of liquids). However, it uses a DPD chlorine test, but Palintest has a FAS-DPD chlorine test now as well though it may only be for the U.S.

Thanks for both the alternative test kit suggestions, I will give one a try but that will take a few days/weeks, for now I still have this discrepancy between test strips and OTO, currently the test strips show 1ppm FC&TC but the OTO shows 4ppm, I just don't get it

Nothing to get....there is a reason many people refer to the strips as 'guess strips' and you have seen it first hand. If you are testing TC and the strips are reading lower than the OTO believe the OTO. It is a bullet proof test. If you are trying to compare strip reading FC then you are comparing apples and oragnes since OTO only meansures TC.

[macgd016]

Nothing to get....there is a reason many people refer to the strips as 'guess strips' and you have seen it first hand. If you are testing TC and the strips are reading lower than the OTO believe the OTO. It is a bullet proof test. If you are trying to compare strip reading FC then you are comparing apples and oragnes since OTO only meansures TC.

As I have said earlier all three of my test strips measure both FC & TC so although you choose to call them 'guess strips' (a term I have not come across before indecently) they are showing the same low TC & FC readings and it is unlikely that all three are incorrect. It would seem therefore that it is OTO that is out of step and although you say OTO is Bullet Proof there will be a reason for this discrepancy and I had hoped that someone on this forum might have come across a similar situation in the past so that I could gain from their experience. Not to worry though I will work it out and report it here in due course.

[waterbear]

Nothing to get....there is a reason many people refer to the strips as 'guess strips' and you have seen it first hand. If you are testing TC and the strips are reading lower than the OTO believe the OTO. It is a bullet proof test. If you are trying to compare strip reading FC then you are comparing apples and oragnes since OTO only meansures TC.

As I have said earlier all three of my test strips measure both FC & TC so although you choose to call them 'guess strips' (a term I have not come across before indecently) they are showing the same low TC & FC readings and it is unlikely that all three are incorrect. It would seem therefore that it is OTO that is out of step and although you say OTO is Bullet Proof there will be a reason for this discrepancy and I had hoped that someone on this forum might have come across a similar situation in the past so that I could gain from their experience. Not to worry though I will work it out and report it here in due course.

Understand that I have experience with water testing ( and not just pools) that goes back to the 70's and I am quite familiar with the chemistry involved. The most likely explanation is that your strips are not fresh or have been stored under less than ideal conditions as this can cause what you are seeing. It it also more common than you would think. Do your strips turn to shades of pink and red? If so they are DPD based. If they change to shades of purple then they are syringaldazine/vanillan based tests (modified FACTS testing) and test for FC and are ususally coupled with a cupric/OTO test on the strip for TC (yellow-green colors). These tests are susceptible to atmospheric oxygen, moisture, heat, and light. It is the nature of the beast with a strip.

Once again I will say that, even though you have tried multiple test strips I would trust the OTO test. IF you want to check this out get a test based on either liquid reagents, tablets, or pillows of reagent that use DPD or, even better, get an FAS-DPD titration test for chlorine and you will see what I am talking about.

As far as coming across this before, I have on many occasions and not just with the chlorine tests. CYA testing by strips is notorius for being inaccurate and pH testing just does not have enough precision to give you any worthwile information (unless you use a speciality pH only strip that is calibrated in .2 increments, which is not the norm.)