How accurate are liquid drop test kits?

Most probes come calibrated, if you want to check calibration you would need get some PH standard it comes in 4,7 and 10. I would buy at least 2 standards 4 and 7, 4 standard is pink and 7 standard is yellow. This way if your Cal is off you can run a 2 point Cal on your instrument. The reason I wouldnt buy the 10 standard is because its the most unstable of the 3 standards and needs to be replaced before you can use it up.

Drip test results make you match the color of the test to a color chart and without a spectrometer machine you can deffintly be off easily by 5 tenths.

does your PH probe have a glass bulb or does it measure mV via a electronic chip?

If it has a glass bulb inspect by turning the instrument upside down, if you can see an air bubble in the solution inside the bulb then you would have a defective instrument.

Hope this helps

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chinnp said:

I had it in the tank while at work today and it went up to 7.5 and held there. That's consistent with the 7.6 I'm reading on the drop test and easily accountable by the color on the card. 7.5 is not going to be much different from 7.6 colorwise. I put it back in the 7.0 solution they provided and came back 30 mins later and it was reading 7.1 so perhaps I'm merely being impatient.

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Using the API Master kit when doing PH in my tank it reads 7.6 (to me) so I thought that was odd because a different test kit I had always gave me a PH of 7, as did my LFS whenever I had water tested there. So I ran the High PH test and it it came up yellow, which would indicate it did not register on the high PH scale. This happened on both my tanks.

Sooooo... :y220d:

chinnp said:

So the moral of the story is that all tanks have a PH and there is no way to measure it accurately.

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Half true, every tank has a PH value and you can accurately measure your PH.

PH is more of a continuis measurement, so you should not focus on one known measure. Test everyday then after 5 or so days you will have an average of your pH.

Your PH may change after a water change as well. Also the more you use your meter the more it will cime to you.



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chinnp said:

Off by .5 though? I'm basically needing to determine if the guy telling me this is blowing smoke at me because his product isn't working or if he's 100% correct.

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Calibrate the unit against known stock calibration solutions, which are available from several suppliers. Then you'll know if the meter and probe are accurate. This week. Probes wear/age over time and calibrations drift. They also have to be stored correctly if not in use.
If you are using the meter for CO2, keep in mind there can be a 1.5 change in the pH over the course of 24 hours.

chinnp said:

So the moral of the story is that all tanks have a PH and there is no way to measure it accurately.

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There are lots of accurate test kits. Are you willing to spend $35.00 to $100.00 (per test) for an, at the moment, precise measurement that isn't really important? How about $10.00 (per test) for one that won't hold up in court, but is very accurate? Some tech minded (and very anal) fish keepers or breeders of very expensive fish would pay the cost. Most of the latter would expect to make it back on F2 sales.

Reasonable is what most of us use and rely on. If you'd like instructions on calibrating a liquid test kit, do a search on http://www.plantedtank.net/forums/
A regular user, name Hoppy, posted a detailed description a year or four, back.