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Thread: tf 100 test cylinder

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    no-mas's Avatar
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    tf 100 test cylinder

    So I come home today and read a post where somebody tested the TA and pH of rainwater - It rained here about 3/4" today, so I figure seems like a good idea, I'll do the same. I expect 0 TA, but who knows? Anyway, I empty my rain gauge into a 50ml graduated cylinder and pour out the excess 'til my cylinder has 25ml, and go in to test the TA. I pour it into the test cylinder of my tf100, and it reads 29ml.

    OK, thinking maybe I screwed up, I pour my sample back into my graduated cylinder - 25ml. Back into the test cylinder - 29ml. Hmmm. What does this mean for my TA test, or my CH test?

    Now, I fill my graduated cylinder to the 10ml mark, then fill my "chlorine only" test cylinder - 13ml. So, what does this mean for my FC and CC tests?

    I trust my graduated cylinder. Come to find out, my FC may have been a little low because I've unknowingly been testing with not enough sample.

    Has anybody calibrated their test cylinder to a known standard? Hadn't I come across some mustard algae recently - I would have thought that this finding is relatively meaningless - but maybe it's not.
    18k gal inground, everbrite finish, 505 sq ft; 1.5 hp two speed whisperflow; rheem 5100ti 100k btu heat pump; 3 sheer descent falls; DE filter; swg (cell out and using trichlor for now)

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    Re: tf 100 test cylinder

    I had a 60ml syringe that I use to pull water out of my pool and squirt into the cylinders. I put 10ml of water from the syringe into both cylinders and both registered 11ml. So I don't know if my syringe is off or my cylinders.

    I tried the same with 40ml into each cylinder and they both registered about 43ml. So both of mine appear to be the same size, but they might not be entirely accurate.

    I bet for most of the tests it doesn't matter.. but someone more intelligent on that can respond..
    ~13000 inground plaster
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    Re: tf 100 test cylinder

    I noticed the same thing a while back. In my opinion, if you are only comparing your numbers to your own results it isn't an issue. But, I also think that the results are not entirely accurate. Personally, I use the amount that is really 10ml or 25ml for all my tests.
    24ft AGP 52in deep ~13,500 gal
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    425 gal stand alone QCA Hot Tub 15-20 yrs old

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    Re: tf 100 test cylinder

    It was proven a while back that the markings on some of the TF100 vials are off. What I did was to use a sharpie to mark the correct level on the vials.
    7,500 gal, IG pool, L shape 22' x 15', 1.5 hp pump, cartridge filter, AquaPlus SWG/Controller, Pebble-Tec liner.

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    MikeInTN's Avatar
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    Re: tf 100 test cylinder

    Most, if not all, of the tests have a +/- factor to them. I personally wouldn't worry about it, I doubt two milliliters here or there is enough to skew the results that badly.
    24' x 52" AGP - approx 13,500 gallons
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    Re: tf 100 test cylinder

    I don't want to insult anyone, but is it possible that the vials that are a different size / shape / material would have a meniscus of differing sizes and that the error is in not taking that into account?

    After a lot of squinting I've decided to that to get 10 Ml in my "chlorine only" tube, I need the water line at 12ml because that seems to put the bottom of the meniscus at 10ml.
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    Re: tf 100 test cylinder

    Quote Originally Posted by MikeInTN
    Most, if not all, of the tests have a +/- factor to them. I personally wouldn't worry about it, I doubt two milliliters here or there is enough to skew the results that badly.
    If it's "really" 11ml instead of 10ml then your reading will 10% low. So, FC 10 will read as FC 9. I am not worried. Learn how your pool behaves; despite its repeatedly measured CYA 30, I have to keep mine at FC 4+ instead of the "official" FC 2, to stay clean (and we don't use it that much). That's just how my pool behaves, and that's more important than exactly what the number is.

    Quote Originally Posted by CurtisT
    After a lot of squinting I've decided to that to get 10 Ml in my "chlorine only" tube, I need the water line at 12ml because that seems to put the bottom of the meniscus at 10ml.
    The bottom of the meniscus is all that matters. I don't even know what the "water line" is for my cylinder, because that's not what I'm looking at!
    --paulr
    BBB "Intermediate Swimmer"
    IG plaster pool 18.5K gal, Hayward Pro-Grid DE filter, 3/4 HP Hydramax II; Polaris 380, 3/4 HP booster
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    no-mas's Avatar
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    Re: tf 100 test cylinder

    Quote Originally Posted by CurtisT
    I don't want to insult anyone, but is it possible that the vials that are a different size / shape / material would have a meniscus of differing sizes and that the error is in not taking that into account?

    After a lot of squinting I've decided to that to get 10 Ml in my "chlorine only" tube, I need the water line at 12ml because that seems to put the bottom of the meniscus at 10ml.
    No insult taken - The bottom of the meniscus is the correct way to read a liquid volume. Yesterday, I poured 10 ml from my tf100 cylinder to my graduated cylinder - where it measured 7 ml. That is a 30% discrepancy. I think, therefore, that my chlorine has in actuality been higher than what I've tested, since I've been testing with a 7ml sample instead of 10ml. I guess that my algae has been a result of my letting the chlorine drop too low, or not running the pump long enough, since the kit was giving me a low chlorine reading rather than a high one (I think ).
    18k gal inground, everbrite finish, 505 sq ft; 1.5 hp two speed whisperflow; rheem 5100ti 100k btu heat pump; 3 sheer descent falls; DE filter; swg (cell out and using trichlor for now)

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    Re: tf 100 test cylinder

    Well, if each drop counts as 0.2ppm in a 25ml sample and 0.5 in a 10ml sample, then each drop is about 0.7 in a 7ml sample.

    It would be worth checking the cylinder at various levels to see whether it's constantly off by 3ml (easy to compensate), or whether the 3ml difference at the 10ml line expands to more at the 25ml line.

    I compared my TF100 cylinders to a Taylor cylinder from a Leslie's DPD Complete kit; 10ml in the Taylor came to about 11 in the TF100. Taylor's 25 came to between 26 and 27 in the TF100. The meniscus in the Taylor cylinder was much flatter than in the TF100, for whatever that's worth.

    If it's within 10% I'm not going to worry about it; 30% is not good, though.
    --paulr
    BBB "Intermediate Swimmer"
    IG plaster pool 18.5K gal, Hayward Pro-Grid DE filter, 3/4 HP Hydramax II; Polaris 380, 3/4 HP booster
    AG spa 325 gal, probably Sundance of some kind
    Water testing instructions on one page

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    Re: tf 100 test cylinder

    This subject was brought up last year:

    test-vial-graduations-t8966.html

    Here was my findings last year:

    I noticed the same thing. I have found that to get 10ml, you need to fill it to the 12ml mark. Also, to fill 25ml of water, one actually has to fill it to the 28ml mark.

    I verified this by three ways. A 10ml glass pipet; Rainin 5 ml pipette (L-5000) and by weight on a analytical balance (resolution 0.001g).
    30K gal. IG Free form
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