Fun with test kits... Overcome visual matching problems - The Planted Tank Forum
 
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post #1 of 14 (permalink) Old 04-15-2008, 07:51 AM Thread Starter
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Post Fun with test kits... Overcome visual matching problems

Introduction:

I don't know if this will be of any interest to anyone... but I'd like to share the results of my little science project involving a common nitrate test kit. I'm new to the forum and hope I'm not repeating something that's been overdone. Apologies in advance... Also, I appreciate any comments and ideas!

My Observation:

Everyone knows that it's sometimes really hard to use a test kit and match your resulting sample to one of the colors on the printed color chart that comes with the test kit. This problem stems from the fact that the color chart is reflected light from a printed medium, and the sample vile is transmitting light through water - two completely different mediums! Even under optimal viewing conditions and viewing angles, it can be hard to discern subtle color differences - "Ummm, <squints> Do I have 3ppm nitrate or 6ppm nitrate?" And I question, "Can my test kit even resolve small differences of nitrates?"

My Idea:

This really isn't just about nitrates, it's about any water parameter that has a test kit which requires visual color matching to get the result. But nitrate is the example here. Since I recently started a dosing regime (yay!), I really wanted to observe how my tanks consume nitrates and I needed to know if an "average" test kit would allow me to do that. I figured if I could remove the "human" visual complexities, then I might be able to get better performance out of my test kit and discern smaller intervals in the nitrate concentrations.

I have the perception that most people serious about testing their water parameters would, first and foremost, test their test kit against a "known" concentration - to see if it's even working correctly. But I decided to take that a step further and try to improve the visual matching aspect involved in these types of test kits.

My idea was to carefully create several known concentrations of nitrate solutions, test them, and then photograph these together with the printed color chart that comes with the test kit. IF the whole scenario was lit and photographed with care, it would be possible to create a better match using a digital image and see how the test kit was really performing.


The Results:

Here is the result of my experiment... the photograph of the tested samples together with the color chart. (For setup details, see separate section below.) The small squares of color in the test tubes are simply areas cut-n-pasted directly from the corresponding color chart swatches on the right side of the image. Please let me know if image does not appear below...



My first reaction was, "Wow. - Those colors are pretty freak'n close!" My second reaction was to notice how different the color swatches appear when they are separated away from the color chart. For example, the yellow color for 0ppm looks much more vivid (saturated) on the color chart than it does when placed as a little square above the water sample - but it's a direct copy from that swatch. (Check it yourself! Copy the image and use a paint program to move the little squares to their corresponding color on the chart.) Needless to say, I was pretty darn satisfied with the relative accuracy of this particular test kit (Aquarium Pharmaceuticals). <Who knew!> But the implications of this little experiment are even more exciting...

Expanding on the Results:

Once I verified that the test kit (two years old!!) was working correctly, I knew that I could completely remove the color chart from the visual matching equation. For example, if I always perform a 0ppm and a 5ppm "known" test along with my tank samples, then all I need to do is compare the tank samples to the "known" samples and easily see if I'm over or under my 5ppm target. In other words, match to the colors of other test tubes, not the color chart. Same medium, easier matching.

Alternatively, if I use the EXACT photo setup (lights, exposure, position, lens, etc.), then I could photograph my tank samples and literally cut and paste the resulting image colors into my reference image to see where they match up!

Another extension would be to create known concentrations of nitrate from 0ppm-10ppm in 1ppm increments, then photograph that set of samples and use it as a reference image against other photographed tank samples. Your test kit can probably resolve those small differences, it's just that it's difficult for us to discern the color difference. The digital reference image can really help. (But you gotta be a total nerd to do it. Like me.)

Notes On Photo Setup:

Simple part: I used a block of wood and drilled holes big enough to accommodate the test tubes. I used tape and thin piece of balsa wood to secure color chart.

The lighting part: The scene is lit from both the front and back with "soft boxes" (very EVEN light). Next, if you have it, use the histogram feature of your digital camera to make sure you are not clipping (over exposing). Technically it's best to use lights that are close to 6500K in color temperature because this is how the manufacturers design and verify the color chart to avoid things like metamerism -- that's when the same printed colors look different under different kinds of light sources. I was careful to match the intensity of the back light to the apparent reflected values on the front of color chart. Next, position the front light to avoid any reflections in the glass and on the color chart. Do not use a front mounted camera flash... shoot long exposures if you have to. The key is even light from all sides with a sufficient back light intensity and a non-overpowering front light.

The camera part: Nikon D200, 19-28mm lens. Exposure: f29, 1/250sec. Two strobes with mounted softboxes. Two white foamcore bounce cards.

The hard part: Of course, it's always more complicated and technical than I just outlined above. But even so, this is not meant to be a technical method of color matching... the actual process of color matching is severely more complicated! It's just an idea to create a consistent viewing environment and help discern small color differences.

It makes for a great Saturday project and really gets you familiar with your favorite analog test kit.

Jeremy Squires, Toronto, ON
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Last edited by i4x4nMore; 04-15-2008 at 06:43 PM. Reason: spelling
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post #2 of 14 (permalink) Old 04-15-2008, 08:43 AM
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Pretty impressive!


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post #3 of 14 (permalink) Old 04-15-2008, 10:44 AM
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wow, that is awesome, i have a lot of problems matching colours as i have glasses and i think they distort colour for me.
With that said, i think the 20ppm vial is closer in match to the 10ppm colour shown on the card. What a mistake i would make if i were to add more nitrates thinking it was 10ppm instead of 20ppm. Now i know why i don't do testing and rely on how the plants are looking and growing instead.

Cheers
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post #4 of 14 (permalink) Old 04-15-2008, 09:04 PM
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That is pretty cool! Instant calibration... I agree with Squid about the 10ppm vs 20ppm issue if the vial were stand-alone against the card!





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post #5 of 14 (permalink) Old 04-16-2008, 05:23 AM Thread Starter
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re: comments

Thanks for the comments. I did discover that as the nitrate concentration goes beyond 20ppm, the dark red color gets very difficult to delineate.

I'm curious based on your comments: Are you really in the habit of adding and maintaining MORE than 10ppm nitrates in your tanks? To me, the test kit operates well in the 5ppm-20ppm range. I would just interpret the darker red colors as a "red flag" (hahah, NPI!) to indicate that I over dosed the tank with nitrates - or something in the tank was severely decaying.


Cheers!

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post #6 of 14 (permalink) Old 04-16-2008, 05:43 AM
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Very nice post.

5ppm is pretty low for nitrates, IMO. Most go for 10-15ppm and up to 20ppm.
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post #7 of 14 (permalink) Old 04-16-2008, 05:49 AM
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I actually did this test myself way back when. I didn't take any photos though, d'oh. It's a good way to both calibrate the test kit and give some memory as to what the colors really look like.

I try to keep at least 10ppm at all times, but it isn't something I ever really test, it's more just adding 5ppm everyday. EI is just so lovely that way, one doesn't need to worry about testing, the weekly 50% water change will work to correct any overage, the goal is to just make sure there's at least enough.

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post #8 of 14 (permalink) Old 04-16-2008, 05:53 AM Thread Starter
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Quote:
Originally Posted by macclellan View Post
5ppm is pretty low for nitrates, IMO. Most go for 10-15ppm and up to 20ppm.
Thanks! Along with your post, I'm starting to get that impression... about maintaining higher nitrates than 5ppm. I have to admit that I'm still one of those converts that is gun-shy when it comes to nitrates and phosphates. There's so much bad info and misinterpreted info about things that cause algae. When I first started dosing 5ppm nitrates, I thought was being a rebel and gonna create some killer strains of turbo-algae! To my surprise, all that 5ppm of nitrate was gone the next day!... and the next... and the next... Who knew?!

Cheers!

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post #9 of 14 (permalink) Old 04-20-2008, 01:52 AM
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i REALLY wish there were some type of digital read out for all the test

I'm color blind and differentiating between those little retarded color squares and the vile is hard and i always resort to asking the person nearest me. its frustrating
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post #10 of 14 (permalink) Old 04-20-2008, 01:57 AM
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Oh, but there is... they're called Colorimeters, they just aren't exactly, uhm, affordable when compared to this sort of test.

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post #11 of 14 (permalink) Old 04-29-2008, 01:38 AM
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Jeremy,

Any plans to work this experiment with other test kits or tests?

AC

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post #12 of 14 (permalink) Old 04-29-2008, 08:09 PM
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I have question about how people hold the tube up to the card. I am also trying to monitor my nitrates closely to help with algae. My question is do you hold the tube against the card or a little in front of it. If I hold it against the card it reads 20ppm, if I just move it away from the card slightly it reads 10ppm. Which reading do you think is right. thanks in advance for any replies.
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post #13 of 14 (permalink) Old 04-29-2008, 08:38 PM
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Slightly away with a very bright white light. I put them on a sheet of paper on my window sill in full sunlight next to the card.
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post #14 of 14 (permalink) Old 04-29-2008, 08:59 PM
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3 things:

1) Good Job!

2) Has anyone ever figured out how to compare the vial to the card? Is it held against the card (white area)? An inch away from the card? Beside the card? Seeing light through it? See the light reflecting on it? Sheesh, there has to be 20 different possibilities. I emailed API this question many moons ago--of course, no response.

3) I don't think a lot of people have your photography knowledge/skills. Any chance that you could work with your skills and printer and try to come up with a printable picture like above that we could all just download? I realize that printers vary, but I'm willing to assume some usefulness for the masses here......





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