AP Test Kits... - The Planted Tank Forum
 
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post #1 of 9 (permalink) Old 03-25-2006, 10:29 PM Thread Starter
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AP Test Kits...

This is a question that I have had for a long time:

When reading the results of the AP Test Kits-Are we supposed to hold the vial against the white area of the chart, or just above it...?

Against it--blocks out some light and darkens the result.

Above it doesn't and lightens the result.

Sometimes it makes a difference in trying to read it.

Anybody know for sure?


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post #2 of 9 (permalink) Old 03-26-2006, 12:16 AM
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It really doesn't matter as these tests are not that accurate. Just read it the same way each time and look for the changes from reading to reading.

If you want accuracy, mix up a calibration solution using a precision balance. If you don't have access to one, call your local university and ask if someone in the biology or chemistry dept. will let you measure out some sodium or potassium nitrate and mix it up to be a calibration solution for your fish aquarium test kit.

The AP kits can easily be off 5 ppm either direction from kit to kit.
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post #3 of 9 (permalink) Old 03-26-2006, 12:45 AM
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I hold the testtube against the white card, but with enough light to not create shadows or darken the result. Example - if there is enough daylight I turn my back to a window so the card faces full daylight.

However... I don't know for sure how one is supposed to do it.


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post #4 of 9 (permalink) Old 03-26-2006, 01:03 AM
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The PH test is a color test, not a darkness of the color test. So, I always try to hold that test tube against the white part of the card to try for more accurate color. I find it very, very hard to judge the colors for the higher PH readings.

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post #5 of 9 (permalink) Old 03-26-2006, 01:18 AM Thread Starter
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Quote:
The PH test is a color test, not a darkness of the color test.
That's not quite accurate. I understand what You are saying, but holding the vial against the card darkens the vial--and the color.

I just did a ph test and against the card--its 6.6, but if I move the vial a 1/4"-1/2" away from the card--the light entering the vial "Brightens" it to maybe a 6.4.

Same with nitrates: against the card its a 20ppm, above the card it looks a lot more like 10ppm.

The amount of light effects the color reflecting from the vial. No light = Black.

Give it a try.

I just emailed AP and asked. Just seems like their sight gets more worthless as time goes on..... From past experience: I should hear back from them in a week or so....


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post #6 of 9 (permalink) Old 03-26-2006, 04:34 AM
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With PH you are looking to see the difference between slightly green blue and blue that is almost real blue for the higher PH readings. The lower PH readings I can pick out easy, but not those high ones. And, I still find that I want the test tube so I am looking thru it at the white part of the card, not right up against the card. I also look for light reflecting off the card thru the tube, so I face away from the window. My real problem is probably that I don't want to buy a High range PH test kit. PH is the only subtle color test that I do. KH and GH are easy.

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post #7 of 9 (permalink) Old 03-26-2006, 06:52 AM Thread Starter
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Quote:
And, I still find that I want the test tube so I am looking thru it at the white part of the card, not right up against the card.
That's what I'm talking about: From that description, it sounds like You prefer it just above the card....

You're Right. The KH and Gh are easy. And so are zreo Nitrites, Nitrate, Ammonia, etc.

I can pick the color out--but its effected by the amount of light as described prior. And I've look under sunlight, flourescent, incadencent....

Some I can pinpoint, and others I can pinpoint down to two--depending upon how I hold the vial....


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post #8 of 9 (permalink) Old 03-26-2006, 01:15 PM
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The pH test in particular is prone to false readings depending on whether you look at it under incandescent, flourescent, or daylight illumination. I try to use daylight.

On the ammonia, nitrate and phosphate test, I find it helpful to compare the sample to the zero color on the card immediately upon putting reagents in the tube, then again after the recommended time. This makes it easier to gauge low readings.
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post #9 of 9 (permalink) Old 03-31-2006, 04:24 AM
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I'd be interested to see what AP says. I actually had the same question earlier tonight.


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