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Digital pH meters

Discussion in 'CO2 Enrichment' started by scottward, Jul 14, 2010.

  1. scottward

    scottward Guru Class Expert

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    Hi guys.

    After a bit of quick research I can see that electronic CO2 meters are very expensive...

    I have a chemical pH test kit, but find it difficult to read and all too easy to interpret the colour as different values coupled with the poor resolution at the lower pH levels...usual criticisms...

    So I was thinking of buying an electronic pH meter, as they aren't too badly priced (I can pick one up for under $100 AU).

    Are there any specific types, brands of these meters that are better, or are they all essentially the same?

    Could a pH meter be dragged about the aquarium to get some idea of relative CO2 levels? I would expect the pH to be lower in the open water, higher in the plant beds where the CO2 levels are lower. kH would be constant throughout the tank correct?

    Scott.
     
  2. Gerryd

    Gerryd Plant Guru Team
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  3. Gbark

    Gbark Guru Class Expert

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    Any ph meter should be ok, i use one that has the pH probe and Temp probe seperate, some come combined in one.

    Just ensure that you calibrate it. i do it once a week on water change. ;)
     
  4. scottward

    scottward Guru Class Expert

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    Thanks for the replies guys.

    How are these things typically calibrated? I suppose you have to purchase some fluid that is of a set pH and dip the probes in it? Do they usually come with this fluid? Can you keep reusing the same fluid or do you have to keep replacing it at each callibration?

    Oh - also - are these things a pain to clean (and require regular cleaning)?

    Scott.
     
  5. Gerryd

    Gerryd Plant Guru Team
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    Scott,

    All that info is in the link I provided :)

    They do include TWO fluids for a low and high calibration... It is easy to calibrate and the instructions are very clear...

    By doing a dual stage calibration it ensures a better accuracy rate,,

    Just have to watch the probes that they don't get algae covered....

    I wiped mine weekly.. not sure if a quick excel dip would hurt, but never tried it...
     
  6. scottward

    scottward Guru Class Expert

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    Thanks Gerry. I hadn't actually looked at the link you provided yet (am looking at this at work), obviously. ;-)

    Will check out your link soon though.

    Much more fun than working.

    There are tons of electronic pH meters on eBay, this is the cheapest one on there:
    http://cgi.ebay.com.au/DIGITAL-PH-PEN-WATERPROOF-TESTER-HYDROPONIC-METER-/330445260164?cmd=ViewItem&pt=AU_Pool_Spa_Beach&hash=item4cf0128584

    Do you think something like this for around $20 would actually be any good?

    I know you get what you pay for, but are these devices so incredibly simple that the dearer brands are only dearer because of the brand name badge on them, but still come out of China anyway?

    How exactly do these things work? Is it just a simple electronic circuit for which no sophisticated or high-quality circuitry is required?

    Scott.
     
  7. Oreo

    Oreo Guru Class Expert

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    The pH meter is indeed a fairly simple circuit but some are built better then others. The nicer ones will have a temperature probe and automatically compensate the pH reading for the temperature but this isn't critical for our use. Some will also have a 3 point calibration vs. a 2 point. I'd expect the 3 point calibration to be more accurate & more expensive but again, not critical for our use. The probes on the other hand come in a wide variety of quality & design but you can be sure any bargain unit will come with a cheap probe if it comes with one at all. Cheap probes run ~$50 and will last up to a year but probably less. A "double junction" probe would be slightly better for our purposes but they cost a bit more.

    As for the calibration solution, this is the only option that makes any sense in my mind: http://www.hach.com/hc/browse.exploded.category.products/PRODCAT0640/NewLinkLabel=pH+Buffer+Pillows
    They are powder pillows that you mix with distilled water to give you your calibration / buffer solution. These are by far the cheapest unit cost and are lab grade quality.

    Here's a great site for more info on pH meters & probes: http://www.ph-meter.info/
     
  8. james.folsom

    james.folsom Guest

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    deleted deleted
     
    #8 james.folsom, Jul 15, 2010
    Last edited: Aug 26, 2010
  9. Oreo

    Oreo Guru Class Expert

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    It's not about clogging them. It's about preserving the reference solution. The two junctions are in series, not in parallel, if you will. A single junction probe will allow the ions in the reference solution to leech out of the probe much faster. For in-line / continuous monitoring of aquarium water this is a real issue because the probe is constantly submerged in aquarium water vs. in a lab setting where the probe may be used for a few minutes to take a reading and then placed back into a storage solution. Ultra-high dollar probes will allow for draining & refilling of the reference solution & thus a much longer life-span. Even fancier probes use a salt bridge instead of a permeable junction. As far as clogging the junction goes, the worst thing for our inexpensive probes is to leave the bulb exposed to air long enough for the junction to dry out. That can ruin a probe in a matter of minutes.
     
  10. hbosman

    hbosman Guru Class Expert

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    hmm, since we only need a general reference, that still sounds like too much hastle. I think I will just stick with the drop checker and AP test kit. I only want to see if a change occurred since we use other methods to determine proper CO2 levels ie...proper PH.
     
  11. Oreo

    Oreo Guru Class Expert

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    I don't find mine to be a hassle at all. I mean, calibration is quick & easy and surprisingly only needs to be done every couple of weeks for me. Even though pH is a poor reference of CO2 using hardness charts it's still a fine reference once you learn what pH your water is with 30ppm CO2. For instance, I know that at 6.55 a couple of my fish start gasping at the surface. 6.60 is a safe number. I can see that number lit by LED all the way across the room which is doubly nice considering I'm horribly color blind and determining what is green isn't always easy for me. That pH meter has saved my fish from poor CO2 adjustments twice now.
     
  12. Left C

    Left C Lifetime Members
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    Check this out.

    For aquarium use, my Milwaukee and Pinpoint pH probes are double junction and they aren't lab grade. I have a Hanna pH probe too and it is a double junction probe as well.

    But, a few years ago I took some biotech courses at the local college. Their lab probes were all single junction. LOL
     
  13. hbosman

    hbosman Guru Class Expert

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    Thats a good point. Assuming that KH2PO4 ppm is generally constant for instance, you will know what ppm CO2 a certain ph is in your tank. Using color does suck. Morning light makes the drop checker look one color and then aquarium lights in the afternoon make it look another. There's no way to see the color difference between 6.55 and 6.60.

    Another toy to buy.. Thaanksss! :)
     
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