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Re: V3 #986 How precise is good enough for a pH measurement?



James,

The important difference between pH meters (cheap or otherwise) and chemical indicators is convenience. If you have one or two tanks, stick with the chemicals. If, on the other hand, you have many tanks, particularly if they range widely in pH levels, go with the meter.
It is much easier to go around and test lots of tanks with a meter. It is important to calibrate regularly though, and equally important to store the probe appropriately. Their accuracy is equal to the care with which you use them.
Chemical indicators are much simpler to use with just a couple of tanks and good lighting. No calibration etc. and really cheap.

In practice, the accuracy debate is redundant. Natural bodies of fresh water suffer changes on a daily and seasonal basis and the organisms have developed to survive. The minor difference in accuracy between the two methods won't make any real difference.
It is also impossible to tell which will be more accurate for you, as everything from care of the meter through to the lighting under which you use the chemical tests will have an influence.

I use meters at work (I've worked at a retail aquarium for five years) and at home (where I have kept everything from aquatic plants and fish to reptiles and frogs for twenty or so years). I also use chemical pH tests in both places occasionally. Usually, I'll go for the meter, but I regularly check it's accuracy against a chemical reagent. The meters just make life easier - not many people have to regularly check more than a hundred aquaria at a time, but I'd be willing to bet that they all use a meter most
of the time. Any that don't, have more time and patience than me.

Don't be afraid of some of the cheaper meters. The price difference is only gadget value most of the time. Easy calibration is important, as is replacing the calibration solution regularly (every three to six months is good) A replaceable probe is good, but check the prices -  I'd be inclined to replace the probe yearly.

The difference between 0.1 and 0.01 is in the display, not the probe. Besides, a difference of 0.05 won't be noticed by anyone. Relax, if you couldn't get one, you wouldn't 'need' it. :-)

Herman

>
>
> Date: Thu, 22 Apr 1999 19:36:56 -0400
> From: "James Purchase" <jpurch at interlog_com>
> Subject: How precise is good enough for a pH measurement?
>
> Here's one for the scientifically inclined...
>
> Currently, I use a LaMotte pH test kit which is calibrated in divisions of
> 0.2 pH units. By extrapolation, it isn't too difficult to read the
> comparator to 0.1 pH.
>
> I've been considering buying a Hanna Instruments Piccolo Plus pH tester,
> which has a claimed precision of 0.01 pH and an accuracy of 0.01 pH. It has
> manual 2 point calibration and will automatically compensate for temperature
> variations.
>
> Years ago, when I was still doing salt water tanks, I picked up an el-cheapo
> "pH pen" at a club auction and promptly threw it away due to it's lack of
> accuracy (or was it just because I didn't realize that the thing had to be
> re-calibrated constantly and I was just too much of an idiot to know any
> better at the time?). So I'm rather leery of electronic meters.
>
> Anyway, the Piccolo Plus looks to be a quality piece of equipment and I'm
> wondering if anyone with more experience dealing with electronic pH
> measuring devices can give me an opinion. I'm favouring it over cheaper
> devices due to it's higher precision (0.01 pH for the Piccolo Plus vs. 0.1
> pH for most other units). Is the extra precision worth it?
>
> The pH electrode on this unit is replaceable - how long a service life
> (given proper storage and maintenance of course) can I expect of the
> electrode.
>
> Thanks,
>
> James Purchase
> Toronto
>