Potassium test kit - The Planted Tank Forum
 
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post #1 of 6 (permalink) Old 10-29-2004, 10:54 AM Thread Starter
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Potassium test kit

Anyone tried one of these yet? http://www.aquariumlandscapes.net/aq...-Potassium.cfm

Well, at least my algae is pearling...
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post #2 of 6 (permalink) Old 10-29-2004, 12:00 PM
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I haven't tried it, but let me hazard a guess.

The site does not say HOW they are doing the analysis. I suspect they are still doing a turbidimetric analysis (precipitation of potassium using tetraphenylborate - the solid formed causes the solution to scatter light - the amount of scattered light is measured), but have merely developed a very inexpensive turbidimeter to do the analysis. Coming from the science end of things, I'm surprised they don't mention the range of K they can measure with it (nor do they mention the "proper" level for aquariums).

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2g Mac-quarium. Clown gravel, fluorescent plastic plants, and 2 guppies.
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post #3 of 6 (permalink) Old 10-29-2004, 12:19 PM
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Kevin,

You are correct. And IMHO the kit is another sucker trap.
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post #4 of 6 (permalink) Old 10-29-2004, 01:24 PM
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Is turbidimetric analysis the same thing a spectrophotometer does? Those are such delicate and extremely expensive ($1,000 - $5,000, $10,000+) pieces of equipment. I would doubt a $30 "spectrophotometer" could do the same thing.
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post #5 of 6 (permalink) Old 10-29-2004, 02:47 PM
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Chris:

Spectrophotometers measure the amount of light at a very specific wavelength transmitted through the sample. A turbidimeter only needs to know how much light is scattered (wavelength is relatively unimportant). So to make a turbidimeter, you need a light source (a simple red LED would work), a few lenses (focus light), and a detector (there are some very simple/cheap light detectors out there). Put it all in a box with the light source/sample/detector forming a right angle, put a readout on the front, and you have it.

Precise turbidimeters are still pretty expensive - LaMotte sells one for $720. However, if you sacrifice some of the precision (only use one wavelength, less concern over stray light or stability), you could cut the cost greatly.

For a spectrophotometer you need a light source that provides the specific wavelength(s) you need and then you need to filter/isolate to only allow one wavelength to hit the detector at a time - that is often the expensive part. If your spectrophotometer only looks at one wavelength (not adjustable), you just put in the right light source and filter. If you want to be able to look at a wide range of wavelenghts, you need a white light source and variable wavelength monochromator - much more expensive.

For example, Fisher Scientific sells LaMotte single-parameter colorimeters for $300-$450 each (depends on the chemical to be analyzed), but sells a LaMotte 4-wavelength colorimeter (evidently enough for analysis of at least 16 different chemicals) for $704.24. A true variable-wavelength spectrometer (the Spectronic Genesys 20 - from 325 to 1100nm) goes for $1725.

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72g bowfront planted, CO2, 4x - T5HO, Eheim 2213 and 2217, 2 angels, pristella tetras, blue tetras, betta, albino bristlenose pleco, albino cories. Sword, vals, hygros, ludwigias, java moss and fern, anubias

2g Mac-quarium. Clown gravel, fluorescent plastic plants, and 2 guppies.
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post #6 of 6 (permalink) Old 11-01-2004, 04:28 AM
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I bought the kit a while ago. The kit definitely works, it's a titration based test. However, what they don't tell you on the page is that it only effectively works in measuring Potassium levels between 1-2 ppm. The titration test doesn't use a color, it only uses cloudiness. It comes with a 1 ppm indicator reference, and a 2 ppm indicator reference, so you will be able to tell if your potassium level is at or between 1-2 ppm.

Once the level gets over 2 ppm, the cloudiness of the test results all start to look the same. 5 ppm looks the same as 50 ppm using this test.

So, it is useful to see if you have potassium in your water at all, and if it is at or over 1-2 ppm.

For a planted tank, I believe the recommendation of potassium is between 20-50 ppm. So if you want to make sure for example your potassium levels aren't abnormally high, this test kit will not work for that. Nor will it work if you want to check to see if your potassium is between say 10-15 ppm and you want to up it to 25 ppm.

Seachem tried to tweak this test so that it would work up to 100ppm, but they weren't successful. They say they are still experimenting on trying to come up with a cheap test kit that is accurate up to 100ppm.
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