Nutrafin Nitrate 0.0 to 110.0 Mg/L for Fresh and Saltwater, 80-Tests

I have used this test kit several times to monitor Nitrate in aquariums. It is the one kit that has been thoroughly consistent and accurate. You must use good light though when reading the results and follow the directions to the letter, that is important. I have found that viewing the test bottle against the card in direct sunlight helps to match the result to the closest PPM on the card. It can be a little confusing as the other reviewer claimed, but you are aiming for low readings to begin with and this brand is more accurate than the other cheaper one for Nitrate. And at this price compared to getting it at a chain pet store or LFS it is a great deal!

I used to have the old API test kits and they weren't as precise as this one. Best kit I've found.

Long story short...The color from the test tube can not accurately be placed at any one point on the color chart that is provided. Using a computer to analyze the colors, the hue of my test tube is the same as the hue of the 20 mg/L color on the chart, but the saturation is the closest to the saturation of the 50 mg/L color on the chart, and the "value" is actually below the entire chart (it would correspond to 0.89 mg/L). I don't believe there is any way a human or computer can tell where, on the provided chart, the color of the test tube should fall. No matter how I tried to evaluate the colors (naked eye, computer-evaluated red/green/blue or hue/saturation/value), I was not able to come up with a value for my nitrate level. To me this kit was a complete waste of money, although I did have fun trying (unsuccessfully) to find a way to use their inadequate chart to figure out the nitrate level.Long story long...I test color vision every day and I have great color vision. I also got the opinion of other people and everyone agreed that the color of the test tube, before and after a 50% water change (to make sure I wasn't just off the chart), could not be placed anywhere in the provided chart. I read and re-read the instructions and followed it as best I could, although holding the last (of 3) bottles at a "45 degree angle" causes drops to fall out at a very fast rate and sometimes it is hard to allow only three drops into the test tube (this is not a plastic squeeze bottle, but a glass bottle that you must tilt "at 45 degrees" to allow the solution to drip out after shaking for 30 seconds). Personally, I think holding it at 30 or 20 degrees is much easier, but I'm not sure if that changes the size of the drops or not, so I just do what the directions say and throw everything out if more than 3 drops get into the test tube.Before I did a water change, the vivid violet color of the test tube was much different than any of the desaturated colors on the card, which ranged from light pink to dark purple/maroon. I did a 50% water change, thinking that maybe I was just off the chart, and the color of the test tube became more pale, but still did not match anything on the chart. I asked other people and they also had no idea where on the chart my test tube was. There is a limit on what the human eye can do in terms of color and I thought I would take human judgement out of the equation.I got the best lighting I could - difficult because this cylindrical test tube focuses light into a bright vertical beam behind it leaving dark areas near the edges and a much brighter color near the center of the tube when you hold it in front of the white area on the chart. Finally, I got it situated so the color was mostly uniform when looking through the test tube. I then took a digital photo of the test tube held against the white area on the color chart and analyzed it on my computer. There are many ways to represent colors. I used HSV (hue, saturation, value) because the colors on the chart appeared desaturated compared to my more vibrant test tube and I was hoping I could remove that from the equation (also RGB did not provide values that consistently increased or decreased going up or down the chart, where HSV did). I used OpenOffice spreadsheet to create regression equations to correlate each parameter (hue, saturation and value) with nitrate concentration based on the colors provided on the chart. The absolute values of the coefficients of determination were 0.987, 0.913 and 0.996. For those who don't know, if the coefficient of determination (R2) is close to 1, then your equation is very accurate and if it is close to 0 then it is not accurate at all. This means that, in the chart provided with this kit, the hue, saturation and value all change predictably when nitrate concentration changes and you can come up with mathematical formulas that you can plug the values from either H, S or V into and it will give you the nitrate concentration. So, if I record the hue reading from one of the colors on the chart and plug that into the hue formula, it will give me the nitrate concentration that is listed next to that color. This is also the case for saturation and "value." No matter which of the three I use, I always get very close to the numbers listed on the chart. For example, if I analyze the color that is supposed to indicate 20 mg/L on the chart, plugging the hue into the hue equation gives me 18.3 mg/L, saturation gives me 17 and value gives me 20.7 (all pretty close to the correct nitrate concentration of 20).Now, if the colors on this chart actually correlated with the possible colors in the test tube, you should also be able to take the hue, saturation or value from the color of the test tube and with the same formulas, come up with the nitrate concentration in the test tube. All three values should give you roughly the same nitrate concentration. So I analyzed the color from my test tube. Using the "value" of my test tube, my nitrates would be 0.89 mg/L. If I use the Hue, my nitrates are estimated at 21.2 mg/L (much higher) and if I use "saturation," my nitrates are 45 mg/L (more than twice what I got from "Hue" and 50 times as high as what I got from "value"). So, using the formulas I derived from the provided chart, the color of my test tube indicates that my nitrates are 1, 20 and 45 depending on what component of the color I use. These numbers are completely different from one another and show that the color of my test tube really wasn't anywhere in the spectrum of colors provided on the chart.No wonder I couldn't look at the color and see where it fit on the chart. The hue of my test tube was the same as the hue on the chart that indicates 20 mg/L, the saturation of my test tube was closest to the saturation on the chart that indicates 50 mg/L and the value of my test tube was actually off the chart low (lower than the value of the 5 mg/L color on the chart). I'm not sure if I just got a bad test kit or if this will be the same for all the kits, but I think I have shown that there is no way to use the color of the test tube and the colors on the provided chart to come up with a nitrate level. I recommend looking for another nitrate test kit.

A failed product.