# API freshwater Nitrate color chart



## PortFan (Mar 26, 2014)

Picked up a new API Nitrate test kit. The 10ppm and 20ppm colors on the card are the same. The 40ppm and 80ppm colors on the card are the same. 
Old card (~5 years old) does show a slight shade difference between 10ppm and 20ppm. Also the old card shows a slight shade difference between 40ppm and 80ppm. The LFS employee said they are all that way. I've done 3X30% (1/week) water changes and I would like to get the Nitrates below 10ppm.
Any suggestions?
Thanks


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## hose91 (Mar 5, 2014)

I agree that the colors are the same as you've noted. Not sure what to do about that. However, I did some interesting reading on water change math recently. Assume you have 20 ppm nitrate per the test. A 30% water change should remove 6 ppm, assuming the water is evenly mixed. You now have a tank full of 14 ppm water. Next week you do another 30% change which removes 4.2 (1.4×3). So now you have 9.8 ppm. Next week you remove only 3 ppm with a 30 % change. So without ANY new nitrates, you're just under 10 ppm after 3 weeks.

Ironically, the lower your nitrates are, the greater volume of water you to remove in order to remove the same mass of nitrate.

So I think I'd test before a water change, then do two 50% changes on back to back days which should get you close to a 75% reduction from your original value (you'll get some nitrate production in the intervening 24 hours).

The caveat would be that you're going to have a similar effect on any buffers you put in, so you'd want to add them during changes to prevent large unwanted swings in other water properties.

I hadn't fully thought through the math before, but there are sort of diminishing returns of small frequent water changes, though there are probably other advantages to doing it that way.


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## workharddieproud (Nov 7, 2013)

My test kit is less than a year old, I got great eye sight, I mean eagle eyes and my shades from 10 to 20 and 40 to 80 are a slight difference and yes very slight, why I don't know and makes no sense. As far as nitrate levels, mine been hanging around 40 and I've tried allot of stuff to lower them with no luck, but again for the last 4 days I'm trying something else. Not telling what it is till I see a difference. Now the debateable part, I read a couple of articles that nitrate levels to low for long periods of time can be just as harmful as them being to high for long periods and I just now sent a email to a marine/fish scientist and asking about it, I'm NOT a expert so don't take my adivce on nitrates as I do want mine lower than 40ppm anyways. This is my first fish tank ever and I grossly over spent on many things just from seeking advice and reading and listening to allot of mumbo jumbo online. Anyway, good luck and sorry for the long reply with not much help. I do wish on these test kits they would be easier to read.


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## partsrep (Mar 14, 2005)

The API kits are vaguely accurate, but in aquarium keeping are sufficient. It can easily tell you the difference between acceptable levels of nitrate or elevated levels of nitrate. Keep in mind nitrates are a by-product of nitrites and as long as your tank is alive there will always be nitrate production. The trick is to keep it under control with proper maintenance, tank cleaning, water changes, and avoid over-feeding.

A simple solution to reading the nitrate chart, if it's red do a water change. If it's orange, you are OK.


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## Vincenzo (Mar 6, 2014)

Colorimetric methods are quick and easy for non-professionals, i.e., swimming pools and aquariums. Color indicators, except for phenolphthalein, usually cover a range. The other option is meters, expensive and require calibrating. Without calibration they are usless. Best advice is get used to the color variations of the samples. You have to determine what the concentration is from your observation. Establish your baseline, then read all subsequent samples according to that baseline. Best scientific approach.


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## b3w4r3 (Dec 14, 2012)

The color card that comes with the API freshwater master kit is different than the one that comes in the individual API nitrate kit, even though the test is the same. The master kit colors are the same as stated for 10ppm and 20ppm, and also the same for 40ppm and 80ppm, I photoshop compared the colors to verify. The individual test has the better color chart, but I found the following image which is probably better to use than either one alone.










When I hold the test to the screen using this image it's very clear where the sample falls. The fella that made the image used known nitrate concentrations and proper lighting.


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## Vincenzo (Mar 6, 2014)

Excellent work. I too have the master kit. Thanks for the image I will use it. However I have been determining the concentration based on the color variations I observed. Red to yellow and in between. This image confirms that and will mke things much easier.


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