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Calibrating Test Kits - for non-Chemists

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I received a request to write something like this, so: (I hope someone will check this for accuracy.)

Calibrating Test Kits

Calibrating a test kit means using that kit to measure some water samples with known concentrations of the substance being tested for, and using those test results to verify that the test kit is accurate, or to train yourself to recognize the colors that correspond to the concentrations you want to test for. Hobby test kits are not laboratory quality tests. That means we don’t need extreme accuracy in the standard test solutions we use for calibration. If we have a good quality gram scale, with +/-.01 gram accuracy, and good laboratory glass graduated cylinders to measure water volume, there are other articles that tell how to make very accurate standard solutions. The methods described here are for use with ordinary kitchen measuring equipment, measuring spoons and cups. And, the Fertilator calculator on APC was used to easily calculate how to mix these.

Nitrate Test Kits

First, buy a gallon of distilled water from your local grocery store. Use that to make the test standard solutions.

1. Add 1/4 teaspoon - a level measure, not a heaping measure - of KNO3 to 4 cups of distilled water (one quart). This gives you 4 cups of 800 ppm nitrate water.
2. Mix 1/4 cup of that 800 ppm water with 1 3/4 cups of distilled water. This gives you 2 cups of 100 ppm nitrate standard water.
3. Mix one cup of that 100 ppm water with one cup of distilled water. This gives you 2 cups of 50 ppm nitrate standard water.
4. Mix one cup of that 50 ppm water with one cup of distilled water. This gives you 2 cups of 25 ppm nitrate standard water.
5. Mix 1/2 cup of that 25 ppm water with 3/4 cup of distilled water. This gives you 1 1/4 cups of 10 ppm nitrate standard water.
6. Mix 1/4 cup of 25 ppm water with 1 cup of distilled water. This gives you 1 1/4 cups of 5 ppm nitrate standard water.
7. Use your test kit to measure the nitrate concentration in each of the 5,10,25, and 50 ppm nitrate standards. If you wish, add the 100 ppm standard to that set.
8. Compare the colors of those to the color card for your kit, and either verify the accuracy of the kit, or use those colors to train yourself to recognize the colors.

Your nitrate test kit is now calibrated. You can store the standard solutions in tightly sealed bottles for an indefinite period of time for future calibrations. Ideally, you calibrate the kit each time you use it.

Phosphate Test Kits

First, buy a gallon of distilled water from your local grocery store. Use that to make the test standard solutions.

1. Add 1/4 teaspoon - a level measure, not a heaping measure - of KH2PO4 to 4 cups of distilled water (one quart). This gives you 4 cups of 1000 ppm phosphate water.
2. Mix 1/4 cup of that 1000 ppm water with 2 1/4 cups of distilled water. This gives you 2 1/2 cups of 100 ppm phosphate standard water.
3. Mix one cup of that 100 ppm water with one cup of distilled water. This gives you 2 cups of 50 ppm phosphate standard water.
4. Mix one cup of that 50 ppm water with one cup of distilled water. This gives you 2 cups of 25 ppm phosphate standard water.
5. Mix 1/2 cup of that 25 ppm water with 3/4 cup of distilled water. This gives you 1 1/4 cups of 10 ppm phosphate standard water.
6. Mix 1/4 cup of 25 ppm water with 1 cup of distilled water. This gives you 1 1/4 cups of 5 ppm phosphate standard water.
7. Mix 1/4 cup of 5 ppm water with 1 cup of distilled water. This gives you 1 1/4 cups of 1 ppm phosphate standard water.
8. Use your test kit to measure the phosphate concentration in each of the 1,5,10, and 25 ppm phosphate standards. If you wish, add the 50 ppm standard to that set.
9. Compare the colors of those to the color card for your kit, and either verify the accuracy of the kit, or use those colors to train yourself to recognize the colors.

Your phosphate test kit is now calibrated. You can store the standard solutions in tightly sealed bottles for an indefinite period of time for future calibrations. Ideally, you calibrate the kit each time you use it.

Other Test Kits

To follow, maybe:confused1:
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Discussion Starter · #22 ·
Thread Resurection!!!!!!:icon_eek:


Any new calibrations???

Thanks,
Wes
None, and I don't expect to do any additional ones. Remember, the only purpose for doing this type of calibration is to find out if your test kit readings mean anything. The accuracy you can get this way is very limited. But, it is better than thinking your tank has 50 ppm of PO4 in it, when it really has less than 4 ppm. I don't use test kits at all now, and never did make much use of them, so this was mostly just a challenge for me. I did try to make 4dKH water using the method here, and it measured 3 dKH with my test kit. So, that "proves" that either this calibration method works, but with crude accuracy, which is what I aimed for, or it proves that my KH test kit readings are off. Being an optimist, I assume the former :icon_bigg
 

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Thank you!

Thank you for this awesome calibration. I just think that it is still a little baffling to me. I don't know where to get No3 or the phosphate test product. Is there some obvious source? I am sorry for sounding stupid.

Thank you. Steph
 

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ahhhhhh......what conflicting emotions I had this afternoon, when, after testing nitrates with a 'new' test kit for the last several months and not agreeing with the results, I picked up a galllon of distilled water and made some test solutions! Luckily, the results were very easy to read:
Tank water: yellow
10ppm standard: yellow
25ppm standard: yellow
50ppm standard: yellow

All exactly the same shade even! It was so simple! Now I know that my water is probably kinda close to 10-50ppm +/-50 or so. Thanks API/retailer

(and thank you Hoppy, for making the procedure so user friendly-no sarcasm)

I guess I'll just stick to those water changes, who knew?(well, Tom, I guess)
 

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This looks supurb, and is probably just what I need to help resolve the difference between my tap water (25ppm Nitrate) and the time for a critical water change (50ppm? Nitrate). Two questions please:

1) Can the reference solutions be kept for a few weeks, or will the colours deteriorate?

2) Any chance that somebody could translate the measurements in the recipes into SI units? Many of us don't use cups as volume measures and don't use volume measures (teaspoons) to precisely measure chemical powders.

Edit: Trying to answer 2) myself. Presumably the 'cups' used in the recipes are US cups, i.e. 236.6ml. Now, all I need to do is work out the weight of a teaspoon on Potassium Nitrate (etc)

Peter
 

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Discussion Starter · #26 ·
This looks supurb, and is probably just what I need to help resolve the difference between my tap water (25ppm Nitrate) and the time for a critical water change (50ppm? Nitrate). Two questions please:

1) Can the reference solutions be kept for a few weeks, or will the colours deteriorate?

2) Any chance that somebody could translate the measurements in the recipes into SI units? Many of us don't use cups as volume measures and don't use volume measures (teaspoons) to precisely measure chemical powders.

Edit: Trying to answer 2) myself. Presumably the 'cups' used in the recipes are US cups, i.e. 236.6ml. Now, all I need to do is work out the weight of a teaspoon on Potassium Nitrate (etc)

Peter
I admit I didn't give any thought to the rest of the world where "cups" and "teaspoons" are not easy to measure. All I wanted to do was make it easy for someone with a typical American kitchen to determine if his/her test kit reading meant anything at all. A similar approach could be taken with common metric measuring equipment. I will leave it to you to enjoy working that out:biggrin:
 

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I will leave it to you to enjoy working that out:biggrin:
A challenge! This is taking me back 28 years to my O-Level chemistry class - wow. Check my rusty theory here and then I'll try to work out 'kitchen' units later on ...

Looking at your NO3 example (1/4tsp in 4 cups):
800ppm NO3 = 800mg/l NO3
Molecular mass of NO3 = 62.0, molecular mass KNO3 = 101.1
So: 800mg/l NO3 is equivalent to 800 x (101.1/62.0) = 1304.5mg/l KNO3
If this is right, and 4 cups = 946.4ml, then:
Your 1/4 tsp KNO3 should weigh: 1304.5 * (946.4 / 1000.0) = 1234.5mg
Did I get it right, teacher? :icon_bigg

Peter
 

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Discussion Starter · #28 ·
[/INDENT]Did I get it right, teacher? :icon_bigg

Peter
Unfortunately I didn't keep my scratch pad calculations. As I recall I used a round number for the mass of the fertilizer chemicals per teaspoon. It may have been 4 grams or 5 grams, but I can't recall for sure. So, I don't know if you got it right. It does look like you are using the right logic, so it is probably right.
 

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ahhhhhh......what conflicting emotions I had this afternoon, when, after testing nitrates with a 'new' test kit for the last several months and not agreeing with the results, I picked up a galllon of distilled water and made some test solutions! Luckily, the results were very easy to read:
Tank water: yellow
10ppm standard: yellow
25ppm standard: yellow
50ppm standard: yellow

All exactly the same shade even! It was so simple! Now I know that my water is probably kinda close to 10-50ppm +/-50 or so. Thanks API/retailer...

The bottle labeled #2 is not extra solution
it must be combined with #1 per the instructions to give correct readings
 

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The calibration solutions are usless as you used volume/volume. The volume of water will vary based on temp and the spoons of dry ferts can vary due to compaction differences. Any good lab will use weight/weight as they do not change.I suspect your solutions could vary by as much as 20%
 

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The calibration solutions are usless as you used volume/volume. The volume of water will vary based on temp and the spoons of dry ferts can vary due to compaction differences. Any good lab will use weight/weight as they do not change.I suspect your solutions could vary by as much as 20%
If you have a few minutes to make those corrected adjustments please post the results. It will be gratefully received.
 

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Discussion Starter · #32 ·

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I admit I didn't give any thought to the rest of the world where "cups" and "teaspoons" are not easy to measure. I will leave it to you to enjoy working that out:biggrin:
I did not even have to pull out my calculator, second google hit on "KNO3 reference solution" took me to a page that seems trustworthy enough :hihi:
http://www.bestaquariumregulator.com/reference.htm
Here is a copy and paste from Rex's site (links sometimes change or go dead):

Here's a way to make 10, 20, 30 and 40 ppm NO3 reference solutions:

* Add 1.631 g of KNO3 to 1 L distilled or DI water. This makes a 1000 ppm NO3 solution. (It's really a 1000.29 ppm solution.)
* Add 2 mL of the 1000 ppm solution to 18 mL of distilled or DI water. This makes 20 mL of a 100 ppm NO3 solution.
* Add 15 mL of the 100 ppm solution to 15 mL of distilled or DI water. This makes 30 mL of a 50 ppm NO3 solution.

To make a 10 ppm NO3 solution:
* Add 2 mL of the 50 ppm solution to 8 mL of distilled or DI water. This makes 10 mL of a 10 ppm NO3 solution.

To make a 20 ppm NO3 solution:
* Add 4 mL of the 50 ppm solution to 6 mL of distilled or DI water. This makes 10 mL of a 20 ppm NO3 solution.

To make a 30 ppm NO3 solution:
* Add 6 mL of the 50 ppm solution to 4 mL of distilled or DI water. This makes 10 mL of a 30 ppm NO3 solution.

To make a 40 ppm NO3 solution:
* Add 8 mL of the 50 ppm solution to 2 mL of distilled or DI water. This makes 10 mL of a 40 ppm NO3 solution.

He also explains how to make reference solutions for testing phosphates:

Here's a way to make 1.0, 2.0, 3.0, 4.0 and 5.0 ppm PO4 reference solutions:

* Add 1.433 g of KH2PO4 to 1 L distilled or DI water. This makes a 1000 ppm PO4 solution. (It's really a 1000.09 ppm solution.)

To make 10 mL of a 100 ppm PO4 solution:
* Add 1 mL of the 1000 ppm solution to 9 mL of distilled or DI water.

To make 20 mL of a 10 ppm PO4 solution:
* Add 2 mL of the 100 ppm solution to 18 mL of distilled or DI water.

To make a 1.0 ppm PO4 solution:
* Add 1 mL of the 10 ppm solution to 9 mL of distilled or DI water. This makes 10 mL of a 1.0 ppm PO4 solution.

To make a 2.0 ppm PO4 solution:
* Add 2 mL of the 10 ppm solution to 8 mL of distilled or DI water. This makes 10 mL of a 2.0 ppm PO4 solution.

To make a 3.0 ppm PO4 solution:
* Add 3 mL of the 10 ppm solution to 7 mL of distilled or DI water. This makes 10 mL of a 3.0 ppm PO4 solution.

To make a 4.0 ppm PO4 solution:
* Add 4 mL of the 10 ppm solution to 6 mL of distilled or DI water. This makes 10 mL of a 4.0 ppm PO4 solution.

To make a 5.0 ppm PO4 solution:
* Add 5 mL of the 10 ppm solution to 5 mL of distilled or DI water. This makes 10 mL of a 5.0 ppm PO4 solution.
 

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Discussion Starter · #34 ·
There are several posts in forums that tell how to use grams and liters to make reference solutions. My contribution was a way to do well enough using just what an average American kitchen would have - measuring spoons and cups.
 

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Yeah, the info is extremely accessible, but hadn't actually made it's way into this thread, which happens to be a sticky on one of the largest planted tank forums out there.

Cups and teaspoons are far more relevant to 90% of the members here, but a couple people had asked about alternative measurements, and I thought it would be a good idea to have both options listed in this one thread.
 

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Newbie issue: Non-standard issue of drop-cheker

KH Test Kit
This method, compliments of Cardinal's Keeper (http://www.plantedtank.net/forums/diy/178491-another-diy-4-dkh-solution.html)
(Note: You will need a whole gallon of distilled water to do this.)
1. Start with 6 cups of distilled water in a clean measuring container
<.... selection deleted for brevity...>
8. To make a 2 dKH solution, mix one cup of the 4 dKH solution with one cup of distilled water.
9. To make a 1 dKH solution, mix one cup of the 2 dKH solution with one cup of distilled water.
Hi all of you, and Hoppy in particular. I am a newbie and want to do CO2 injection in an 80G planted aquarium. I don't want my plants to be completely slow-growing and low-tech, and I don't want them to be growing too vigorously either, as with 30ppm of CO2. [Yeah, I'm that Great Moderation guy! :redface:] So, I'm thinking I'll go for moderation, say about 15ppm of CO2, moderate lighting. I have two questions:

(1) Does this approach seem reasonable, or am I forgetting/ignoring something important?
(2) Now the more "techy" question. MOst standard drop-checkers, set up with 4dKH, turn green at 30ppm. This works fine for those who want to keep their tanks at 30ppm CO2, but it wouldn't work well for me. I need an indicator that'll tell me (say go from blue to green) at 15ppm instead of 30ppm. So, looking at Hoppy's above post, I thought, why don't I make a 2dKH solution to put in the drop checker? The charts [ http://freshwateraquariumplants.com/carbondioxidechart.html ] seem to say that 2dKH will get to pH=6.6 at about 15 ppm instead of 30ppm, so this should work for me, right? All I do is put 2dKH standard solution and a few drops of the indicator into the drop-checker, and voila! I calibrate CO2 to keep the solution green without going blue or yellow, just like everybody else does, but I'm keeping it at 15ppm, not 30ppm, right? What am I missing?

Thanks for your help in advance!

-aadro
 

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Discussion Starter · #38 ·
Hi all of you, and Hoppy in particular. I am a newbie and want to do CO2 injection in an 80G planted aquarium. I don't want my plants to be completely slow-growing and low-tech, and I don't want them to be growing too vigorously either, as with 30ppm of CO2. [Yeah, I'm that Great Moderation guy! :redface:] So, I'm thinking I'll go for moderation, say about 15ppm of CO2, moderate lighting. I have two questions:

(1) Does this approach seem reasonable, or am I forgetting/ignoring something important?
(2) Now the more "techy" question. MOst standard drop-checkers, set up with 4dKH, turn green at 30ppm. This works fine for those who want to keep their tanks at 30ppm CO2, but it wouldn't work well for me. I need an indicator that'll tell me (say go from blue to green) at 15ppm instead of 30ppm. So, looking at Hoppy's above post, I thought, why don't I make a 2dKH solution to put in the drop checker? The charts [ http://freshwateraquariumplants.com/carbondioxidechart.html ] seem to say that 2dKH will get to pH=6.6 at about 15 ppm instead of 30ppm, so this should work for me, right? All I do is put 2dKH standard solution and a few drops of the indicator into the drop-checker, and voila! I calibrate CO2 to keep the solution green without going blue or yellow, just like everybody else does, but I'm keeping it at 15ppm, not 30ppm, right? What am I missing?

Thanks for your help in advance!

-aadro
That would work fine, but keep in mind that a drop checker with 4 dKH fluid will be "green" not at 30 ppm, but at something between about 20 and 40 ppm. There is a lot of built in uncertainty with this method, based on the limits of our eyes in seeing green as a specific color, and on the inaccuracy in measuring pH.

I experimented a lot with using a drop checker where yellow was the indication of the right amount of CO2. This was primarily for DIY CO2, where the battle is about getting enough CO2, not about avoiding too much CO2. I ended up using 1.7 dKH fluid. It worked pretty well for me when I was using it, but making 1.7 dKH fluid is hard to do without starting with a good, known KH solution. http://www.plantedtank.net/forums/showthread.php?t=129720
 

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Newbie question on non-standard drop-checker use

Thanks Hoppy! That's useful. So, in that case, I'll be even "safer" using my method, so that if I use 2dKH instead of 4dKH, if the solution goes yellow, I'm less likely to overdose with CO2, although I realize from your comment that I am also likely to under-dose! May eventually need a more accurate meter of some sort!

Any ideas from anybody?
 
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