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Thread: Reading the right Ph

  1. #1
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    Reading the right Ph

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    Its been 2 years that my shrimp stop breeding and started dying.

    Nothing has changed for the past 2 years except i do notice the ph started showing different values.

    With my no-brand ph pen, it shows my ph level 7.1, if i test it again after like 1 min, it show 7.2. If i test it again after another min, it show 7.2. So after 3 test, i presume it is 7.2. Using sera buffer solution, my ph pen reads 7.

    Using sera ph liquid tester, it shows ph 5. So the prob now, if i test my tap water, both give my the same result of 6.8 (sera colour is in between).

    So which do i trust?


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  2. #2
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    Re: Reading the right Ph

    In my experience, if the Sera or API test kits aren't expired they are more accurate.

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  3. #3
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    Re: Reading the right Ph

    I agree with bazz. pH meters need to be calibrated and probes need to be in good condition, to get accurate results, whereas drop test kits always work. Also, pH meters' batteries need to have enough juice to be accurate.

    Why don't you test your pH meter in solutions of a (roughly) known pH, e.g. vinegar, or citric acid, for low pH, plus a sodium bicarbonate solution for high pH? (You might need to google a bit to find out how much sodium bicarbonate is need to obtain a certain pH.) Testing with acidic and alkaline solutions will let you know if your pH meter is reading properly on both the acidic and alkaline ends of the range.

    You could even ask how much it would cost at your local LFS to calibrate your pH meter?

  4. #4
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    Re: Reading the right Ph

    Thanks for the respond. My ph pen was calibrated before testing my fish tank water.

    After testing the water, i calibrated again. Thats the dilemma i am having.

    In my tank, its the sponge filter, active soil, plants and bonsai. There is nothing in my tank that could raise the Ph.

    Alternatively, it could be my soil losing buffer ability but i doubt so as i have added 1 pack of new soil.


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  5. #5
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    Re: Reading the right Ph

    Quote Originally Posted by genki89 View Post
    Thanks for the respond. My ph pen was calibrated before testing my fish tank water.

    After testing the water, i calibrated again. Thats the dilemma i am having.

    In my tank, its the sponge filter, active soil, plants and bonsai. There is nothing in my tank that could raise the Ph.

    Alternatively, it could be my soil losing buffer ability but i doubt so as i have added 1 pack of new soil.


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    About calibration, I vaguely recall this...

    Most meters let you calibrate to 4.0, 7.0 and 10.0 (or roughly thereabout). Each point corresponds to a voltage reading at your probe, and when you calibrate that becomes the new "set point" for that value. If you calibrate your meter using (for example) two calibration solutions, pH 4.0 and pH 7.0, you get two different voltage values, one for each pH value. This lets your meter "plot a curve/line" between pH 4.0 and pH 7.0, so that any voltage reading in between can be "read" as a pH value. A voltage reading beyond either end of your set points can also be read by extrapolating the "line/curve" you already have, e.g. a pH of 3.5, or 8.5 etc, but the accuracy drops, and could be wildly off. So, if you are often measuring alkaline solutions, it is best to calibrate at 7.0 and 10.0 (rather than at 4.0), so that your line/curve and hence your readings are more accurate.

    I don't think you should worry that your soil has lost its ability to bring pH down... your drop test kit is probably accurate as bazz and myself have said earlier. Plus you did already just add one new pack of soil - that should already confirm for you that it's the meter that's off, not the drop test kit!

  6. #6
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    Re: Reading the right Ph

    Hahahahaha ok thanks all. Probably i should return to getting reputable ph test pen.


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  7. #7
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    Re: Reading the right Ph

    Anybody want to buy my baby guppies? I sell one for 20 cents.

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