Nitrates Tested Salifert vs. API

[LBDave]

My current understanding of at-home testing for NO3 nitrate is based on what dw1305 on Planet Catfish posted on the subject. Darrel is a professor and a scientist studying wastewater treatment in addition to being an avid tank keeper.

In a nutshell, API and other home tests can give an indication of the nitrate presence but the actual levels can be up to 10x higher and vary depending what other ions are present in the water being tested because those ions interfere with the measurement to a highly variable degree; also the toxicity associated with such high levels of nitrate often stems not from the nitrate itself but from the preceding nitrite and ammonia.

To begin learning, I'd recommend reading Darrel's posts in these threads and the links he and others (such as TwoTankAmin who is well versed too) provided therein:

ammonia nitrite and nitrate study - PlanetCatfish.com

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High Nitrate - PlanetCatfish.com

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water changes controversy - Page 2 - PlanetCatfish.com

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The links you posted have a lot of information but have not seen the specific reference to the capability or error % of the nitrate test kits.
Perhaps you could reference a specific link.
Here is a test of the Salifert test kit validated with lab test results. Perhaps the inaccuracy you mentioned are due to human error. Any test can be affected by variables such as the steps of the test, contamination, test reagents age etc. For my personal fish keeping I would periodically use both API and Salifert, and take care to follow the directions. If done properly. this will suffice for me.
https://reefhacks.com/how-accurate-are-salifert-test-kits/

 

[Coryloach]

It is not just about the accuracy of the tests. It's the interference with other ions such as chloride. Like the common expression, take the nitrate test result with a grain of salt

I have no problem people checking out water quality by any means they have. It means they care. It is just that there are better ways

 

[LBDave]

The purpose in testing nitrate (for me) on an established aquarium, is to determine how often water changes should be done.
If I change 25% of the tanks water, and in a week, nitrate is already at 50ppm, it means to me, too much time has gone by between water changes, and not enough water was changed.
So instead of a once per week water change, that 50ppm reading tells me I need to change more water at least twice per week.
Or if my goal is a stable tank environment, for example, a constant 5 ppm nitrate as a ceiling. I might have to change 40% every other day .
Same with pH, if my tap is 7.5 pH, but after a week the tank water has dropped to 6.0, it means too much time has gone by, and the nutrients in the water have acidified it more than I feel is healthy, and to have a stabile tank, I need to change water more, and more of it.
pH is a little tricky, if you have plants because pH will fluctuate normally day and night.
S taking and testing for pH the same time of day is a way to determine stability.

Duanes, what is your opinion of the seneye device? I find them invaluable for real time ph and NH3 readings. This is how I quickly caught the mini cycle (probably cause by too much CO2 booster).

 

[Coryloach]

1. Tested with Salifert and wow. Nitrates were 50 or more!
2. Tested with API and sure enough, Nitrates were 40 or more. A little hard to distinguish 40 - 80 difference.
3. Tested my tap water. Looks to be 0.
4. I did about a 60% water change and it loos like Nitrates are about 5 - 10 with the API kit.

I'll give you one further example on the flows of nitrate testing based on the info you provided above.

If your tests were accurate, after the 60% water change water with 0 nitrates, assuming the initial concentration of nitrates was 50ppm as per the information provided above, the nitrate concentration in you tank should have read 20ppm.

In order to achieve a remaining concentration of 5-10 ppm, your water change should have been more like 90 to 80% respectively.

 

[duanes]

Most research on nitrate has been done in the aquaculture industry, and is about how to get enough food into as many fish as possible, in the shortest amount of time, for growth in crowded conditions, using the least amount of resources, and still have the fillets look edible enough to make a profit. As in all industry.
So a little HLLE on a Tilapia, or Bluegill, may be of little consequence when the fish is packaged and ready to cook.
So those high acceptable nitrate numbers for aquacultured fish, might mean something totally different to an aquarist that wants a stunning specimen in a tank, for an extended period of time.
Whether a test says 40 or 50 ppm nitrate, is really negligible when nitrate numbers are that far from the natural conditions fish thrives in.
I've been testing some river and stream numbers here in Panama, and nitrate has been non-detectable on my API test.
When I tested water from Lake Michigan, in the states on a spectrophotometer using the Salifert method the lake averaged, less than 1ppm.

 

[Poseidon2.0]

The best and easiest way in my opinion to measure pollution is still a TDS/Conductivity meter, especially in non-planted tanks where there is no fertilizer dosing. I can't remember testing nitrates for 4-5 years or so and I got the last test just so I do a random check if my "TDS theories" are working.

If one goes by a stable TDS tank vs tap, doing enough water changes to maintain it, there will also be no nitrate rise. In a planted tank the TDS can actually drop further than the tap water, so does the nitrate....

See, if you don't monitor the TDS, that nitrate test maybe telling you the tank has 15ppm nitrate but your TDS could have become double your tap water, meaning pollution has accumulated regardless. Nitrate is just one pollutant..

As @thebiggerthebetter is pointing out in his above post, the nitrate test may not give the true nitrate level. It may be way higher than what the color chart suggests...giving you false confidence. Then one thinks their water quality is fine and contributes their latest fish death to "mystery".

If one is stuck into the nitrate testing, test both nitrate and TDS for a while and see how those are related for yourself..You may notice that your "safe nitrate" levels aren't preventing a TDS rise. The TDS meters sold measure conductivity, i.e. ions dissolved in water including nitrate.

Generally, if the TDS is in line with tap water, so are all other parameters, KH, pH, GH, etc...although you don't know their exact levels and you don't know the exact break down of what the TDS test gives you, you know they're in line with your water used for water changes, which is what matters to the fish health.

I pretty much go by TDS only too (got a couple of devices that read it) and once I know where my tap water is at I go from there. Philly water was 350 ppm NYC 50 ppm so much better for my SA cichlid.

 

[LBDave]

Most research on nitrate has been done in the aquaculture industry, and is about how to get enough food into as many fish as possible, in the shortest amount of time, for growth in crowded conditions, using the least amount of resources, and still have the fillets look edible enough to make a profit. As in all industry.
So a little HLLE on a Tilapia, or Bluegill, may be of little consequence when the fish is packaged and ready to cook.
So those high acceptable nitrate numbers for aquacultured fish, might mean something totally different to an aquarist that wants a stunning specimen in a tank, for an extended period of time.
Whether a test says 40 or 50 ppm nitrate, is really negligible when nitrate numbers are that far from the natural conditions fish thrives in.
I've been testing some river and stream numbers here in Panama, and nitrate has been non-detectable on my API test.
When I tested water from Lake Michigan, in the states on a spectrophotometer using the Salifert method the lake averaged, less than 1ppm.

Not that it really pertains to this thread, but for the last 2 weeks I have cleaned my sump by wiping it with a damp towel and pumping it out along with a 60% tank water change. Along with rinsing the media with Prime treated water. Doing this has brought the nitrate down to 2-5. What's the point? Don't for get to clean your sump! (which you have mentioned in the past).

I pretty much go by TDS only too (got a couple of devices that read it) and once I know where my tap water is at I go from there. Philly water was 350 ppm NYC 50 ppm so much better for my SA cichlid.

Now that I understand. Thanks.

 

[LBDave]

I'll give you one further example on the flows of nitrate testing based on the info you provided above.

If your tests were accurate, after the 60% water change water with 0 nitrates, assuming the initial concentration of nitrates was 50ppm as per the information provided above, the nitrate concentration in you tank should have read 20ppm.

In order to achieve a remaining concentration of 5-10 ppm, your water change should have been more like 90 to 80% respectively.

It was a 60% tank change but not the sump. The test indicated the nitrates went down somewhat but not real low. Which was not unexpected.

 

[squint]

Several techniques have been developed that can detect nitrate down to 1.5 nanomolar in seawater. If I did the math correctly, that's 0.000412023 ppm nitrate. I don't think interference from chloride is that big of a problem...

 

[pacu mom]

I've used API test kits for years. I have a hard time distinguishing between the colors on the test cards, let alone trying to match the color in the test tube with the card. The last test kit had the worse color card yet. I got a Nitrate tester from Hanna Instruments. Calibration is easy enough to do, so I do it every time I test. Accuracy is plus or minus 5, so even if I had a "0" reading, it could actually be 5. So this 0.7 could be 5.7, but I can live with that.