This test kit is almost as much as my pH meter since I run very high light/CO2 and I find that the tank can become Nitrogen limited if I\'m not paying attention. I really believe it is one of the most accurate kits I\'ve ever used. Nitrate test kits are much maligned for their lack of accuracy but when I compare what\'s going on in the tank with the measurements in this kit the test results seem coroborative.
I love the fact that it has 4 calibrated scales matched to the color bands. You can use a 20 ml sample and measure NO3 up to 40 mg/l. If the reading tops out at 40 mg/l you can then dilute the sample in ratios of 1:1, 1:3, and 1:6 to measure up to a theoretical limit of 400 mg/l. This assumes of course that you have RO or DI water with which to dilute the sample. I have tested this by diluting known samples to the three ratios listed above and each time, the appropriate color appeared indicating the proper concentration so it\'s consistent.
I should add that the kit, it\'s test procedures and use of the color bands are identical for either fresh or salt water. At my location the price is 13€ ($20) and that works out to about €0.22 ($0.33 cents) per test.
Another brilliant thing about this kit is that the color bands on the chart are discrete color squares with an arc cut-out which matches the shape of the test vial against a white background. This may seem trivial but it makes a big difference when trying to match the color because it provides a more viewable surface are. The colors are bright, and it is very easy to interprolate when you don\'t have an exact match; Yellow to amber, amber to orange, orange to pink and pink to red. Very logical. The trick to reading the colors though is to look down from above as recommended, but to hold the vial just slightly off the paper, enough for the light to reflect back up to the sample. If you set the vial down it blocks the light, darkens the sample and causes a perceived color shift.
Also what I like about Sera test kits in general is that they have a brief dissertation in the instructions about what values your tank should have, what the causes for high readings are and what to do about it. Again, for the expert this explanation is redundant but it is valuable for beginners. The only negative is that because the instruction set is multilingual (20 languages!) there is precious little room for the text and I really struggled to read it due to the miniscule font size.
The kit contents are; color chart/instructions, two liquid reagents and a powder reagent with a plastic scoop. A little bit of the powder is all you need. If you scoop up too much of the powder it doesn\'t affect the color reading but it doesn\'t dissolve completely, it floats and when looking down at the sample the grey powder is a nuisance.
Like most kits I suppose the usual precautions should be taken; buy from a shop that sells at a high turnover otherwise the reagents might get old. If the layer of dust on the box sitting on the shelf is percievable buy from elswhere. I have had a kit with a bad powder reagent, but that only ever happened once. I knew it was the poweder because when I tried to calibrate it using RO water it gave me a 40 mg/l reading. I used leftover powder from a spent kit and the reading returned a proper 0 mg/l. The powder should be a sivery slate gray color. As I said you should always first calibrate your test kit using samples with known values low mid and high. With this kit though I find that if I get a zero value for RO water it\'s fairly accurate and consistent. The highest shift I\'ve experienced is a 5 mg/l reading on my calibration samples. No problem, simply subtract 5 from every test reading.
The only improvement I would like to see Sera make to this kit is to explain how the reagents actually work and what factors could cause inaccurate readings. For example some kit reagents convert the NO3 to NO2 and then masure the NO2. If the sample already has perceptible NO2 (such as during tank cycling) this would give a false high. If they added this explanation in every language though it would make the font size even smaller!
Easy to read color chart, Repeatability of measurements