pH calibration fluid

Discussion in 'Test Kits, Controllers, Reactors and Dosers' started by Tobes, 1 Jun 2009.

  1. Tobes

    Tobes Retired Moderator

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    Just wondering - what is the pH of "clean" RO/DI water and will it differ from time to time?

    Can someone check it for me with an accurate pH meter/pen?

    My calibration fluid expired :(
     
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  3. Shaun

    Shaun Retired Moderator

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    If you want to use it to check your Ph don't get the fluid. Contact Hanna in Pinetown, it is expensive.
     
  4. Stressed Eric

    Stressed Eric

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    I know the potable water supplied to pmb has a very narrow ph range as it is, so i'd imagine it's as close to constant after filtration too. If you need some ph standards gimme a shout and i'll arrange for ya
     
  5. Reef Maniac

    Reef Maniac MASA Contributor

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    Actually, it will be very inaccurate to try and use RO water for calibration. Due to the pureness of the water, even the slightest contamination could cause the pH to vary dramatically.

    Rather use this recipe: Marine Aquariums of South Africa - View Single Post - Chemical equivalents

    Hennie
     
  6. Tony

    Tony

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    My rhoughts exactly Hennie. Hanna isn't cheap but the bottles are a litre and will last a long time
     
  7. Shaun

    Shaun Retired Moderator

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    They have other bottles the are don't come with a certificate that are much cheaper.
     
  8. Reef Maniac

    Reef Maniac MASA Contributor

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    Be very careful with these - I have tried them in the past (the ones sold in plastic containers looking like milk containers...), and have found that even fresh calibration fluids can differ by more than 1.5 pH from that stated on the bottle.

    IMHO if you are going to use a digital pH meter, rather pay a bit more and get the certified buffers, they are pretty accurate, but it's still worth checking the calibrated instrument with the DIY borax solution as described in the link I posted in my previous post.

    Here's an interesting article by Dr. Randy Holmes-Farley about the inaccuracies he has found comparing different manufacturer's buffer solutions - quite worrying...

    A Comparison of pH Calibration Buffers by Randy Holmes-Farley - Reefkeeping.com

    Hennie
     
  9. Tobes

    Tobes Thread Starter Retired Moderator

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    Hi Uncle Hennie,

    So I need to work out how much Borax to use to make a pH 7 solution since that article only gives the amounts for a pH 10 one?
    Or do you have the correct amounts for a pH 7 solution?

    Sorry, had a beautiful lady science teacher, so did not concentrate too much on the work :p
     
  10. Reef Maniac

    Reef Maniac MASA Contributor

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    No, you can only use this as a "one point" check of your calibrated instrument, if you are not sure if the "old" buffer you have is still accurate - the borax solution should always give a reading of between 9.0 and 9.3, with 9.17 being exactly spot-on at 26°C.

    If your instrument only has one calibration adjuster (all the better ones have 2 points) you can put the probe into the borax solution at 26°C and adjust it to read this value, and it should be reasonably accurate for use in a tank.

    Hennie
     
  11. Tobes

    Tobes Thread Starter Retired Moderator

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    Thanks Oom Hennie
     
  12. ted.vanh

    ted.vanh

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    Try Hanna Instruments who charge R59.00 excl per 500ml bottle with certificate and R39.00 excl per 500ml bottle for local no certificate.
     
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