Nitrate test kits - results confusing

[kilnakorr]

I started out using Aquaforrest NO3 test when cycling the tank.
After the cycle, I have always had low readings around 0.5-2 ppm
I started dosing a little KNO3 to get it up a bit, feeding more and more fish had no effect.
I recently decided to buy another brand test (Tetra), just for reference. Well, seems Aquaforrest reads around 1-ish ppm no matter how much nitrate is present.
The Tetra seemed to be accurate (tested both with a 15ppm KNO3 solution), but the color scale isn't suited for reef tank values.
I just bought the Nyos test ($40+!!), and still have no clue what to trust.
Nyos reading:
Tankwater shows close to 12ppm, but higher (next point on scale is 25?!)
50/50 Tank water and RODI shows 12 ppm
20/80 Tank water and RODI shows between 5 and 12 ppm

Anyone know a Nitrate test kit that can be trusted (within reason).
Or better yet; give some pointers on how to be able to trust the results?

 

[Quietman]

Stop comparing multiple kits?

I don't know Tetra but have used Nyos and AF (and RS an TM, and API). None of them match exactly and some are pretty widely divergent at least on my reading of them. I try very hard to use consistent practices (which I don't think matters that much either - between leveling off spoons and just eyeballing it, I get same result) and follow directions closely.

I like Nyos because I can read the colors the easiest and it's faster than most. I started sleeping much better when I stopped comparing them.

That said...if I had a high reading (I wish...always have had low NO3), or zero reading, I break out the back up (usually TM) and check. It's always been within the limits of good taste, but not usually spot on with other.

There is the Hanna which I've never used. I would assume with all that filtering and reagents that's it does a good job and Hanna reader does eliminate reader error for colors. I just don't need that level of complexity in my life (or maybe I do and I'm in denial).

 

[kilnakorr]

Stop comparing multiple kits?

It is not about comparing kits, or exact results.
But if a test shows 20ppm, then I expect it to show 10ppm, when the concentration is halved.
My problem is, a 20 ppm reading could be 2ppm or 50ppm - I have no idea where I'm at or if the number is rising or falling.

 

[Quietman]

It is not about comparing kits, or exact results.
But if a test shows 20ppm, then I expect it to show 10ppm, when the concentration is halved.
My problem is, a 20 ppm reading could be 2ppm or 50ppm - I have no idea where I'm at or if the number is rising or falling.

My mistake...got the wrong thing out the post. I'll be following, I'm curious as well.

 

[Gtinnel]

You need to make a reference solution with a known nitrate level. I've never made any but there is an older thread where Randy and another user discuss making some. I don't know if itll be helpful or not but here is a link to it.

Help me create a Nitrate Reference Solution

Hello all, Hoping someone can help me out here as I am not finding what I am looking for with a google search. This weekend I purchased a new nitrate test kit. Current test kit ( NYOS ) is reading 3 ppm nitrate and has been fairly consistent over the last 2 months or so ( I am dosing Kno3...

www.reef2reef.com

 

[kilnakorr]

You need to make a reference solution with a known nitrate level.

That is an excellent idea.
My only concern is the 'scaling' won't match.
Meaning, a test might show accurate a slightly higher/lower than the reference, but not at all points. A 10ppm reference might show 12ppm, on the test kit, but a 5ppm might show 1ppm.
If the test isn't consistent or accurate within a certain range, then it's as useful as guessing.

A reference test of 10ppm should read close to 10ppm on the test and a 5ppm reference should read close to 5ppm, but so far every test kit I've tried isn't even close to be consistent in readings.

 

[PatW]

For nitrate, I like Red Sea Pro. It reads down to .25 ppm (so they claim), And I get a faint pink at about half that. But Salifert looks good also and it is CHEAPER.

You could do what is called a “standard curve”. That is you get a standard solution. It is not hard to make up with some Sodium Nitrate and a scale and some salt water. The thing is to make a standard at say 20 ppm. Dilute that 50% for a 10 ppm standard. Dilute again by half for a 5 ppm standard and so on. Then use the test to get the reading on your standards and graph out the results. What you want is a reading of 20 ppm for the 20 ppm standard, 10 ppm for the 10 and so on. Of course, that isn’t going to happen. And you need to do it about 3-5 times for each standard.

But I don’t think that is necessary. On reefs, nitrate concentrations are pretty low generally lower than hobby aquariums. But reefs have flow and the nitrates keep coming in over the reef so they don’t run out. In our tanks, nitrates can go too low. What we want is a test that is sensitive enough so the nitrates are not high enough for algae to run amok. And we want some nitrates for the corals to grow on. People seem to like nitrates at 1 - 5 ppm for SPS and higher for other corals.

All you really need in a test kit is an ability to say “I need more nitrates”, “nitrates look fine” and ”nitrates are too dang high”. All that is required is some sensitivity and some dosage response. Most test kits do that.

 

[Gtinnel]

That is an excellent idea.
My only concern is the 'scaling' won't match.
Meaning, a test might show accurate a slightly higher/lower than the reference, but not at all points. A 10ppm reference might show 12ppm, on the test kit, but a 5ppm might show 1ppm.
If the test isn't consistent or accurate within a certain range, then it's as useful as guessing.

A reference test of 10ppm should read close to 10ppm on the test and a 5ppm reference should read close to 5ppm, but so far every test kit I've tried isn't even close to be consistent in readings.

I'm not sure that I am following the logic. So your saying that you believe that the different test kits are accurate but only within certain ranges? If that's the case just make a solution that matches the level that you want to keep your tank at. Then whichever test shows a correct reading for that sample would be the one I would use on my tank.

I personally would make a solution with a known nitrate of 10ppm and then use that sample to test each kit. Any kit that isn't close to 10 I would quit using. Once I found the kit that I trusted the most I would make samples at different readings and test it at several readings.

For what it's worth I use salifert test kit and it is accurate enough to the best of my knowledge. I get a reading on my tank and then dose potassium nitrate and when I check again I can see the change from dosing.

 

[kilnakorr]

You could do what is called a “standard curve”.

That is not a bad idea.
I'm still not sure I would trust the result.

I'm not sure that I am following the logic. So your saying that you believe that the different test kits are accurate but only within certain ranges?

My issue is, that if a test reads a concentration at say 20 ppm, then I'd expect that a a 50 % and 10% dilution would read 10ppm and 2ppm. If the 10% dilution reads 12 ppm, then the non-diluted could be 120ppm.
At the moment I have 3 different tests, reading Af:1ppm
Nyos:15-ish ppm
Tetra:30-40+ppm.
A 50% dilution I get
Af:1ppm
Nyos:12 ppm
Tetra:25-30ppm

The Af is already proven to be faulty, but between the other results I have somewhere between 15 and 60 ppm.
Nyos shows 15-24ppm and Tetra 30-60ppm
I would at least expect the tests to read within the same error, but it appears not to be so.

 

[Randy Holmes-Farley]

Meaning, a test might show accurate a slightly higher/lower than the reference, but not at all points. A 10ppm reference might show 12ppm, on the test kit, but a 5ppm might show 1ppm.
If the test isn't consistent or accurate within a certain range, then it's as useful as guessing.

I think that sort of deviation is unlikely if the kit ever functions properly.

 

[kilnakorr]

I think that sort of deviation is unlikely if the kit ever functions properly.

Exactly my issue.
BUT, I just realised I have diluted with water from the same little bottle of RODI, since I started my NO3 investigation, of the faulty AF kit.
If I at anytime have somehow contaminated that water, then that would make all the current tests screwed both right and left.

 

[blasterman]

Salifert

These kits are only good within a deviation of +/- 5ppm at most, but thats all you need.

 

[Arthurfarris]

Used Salifert! This kit was so much easier to use with only three steps involved. I do not have to do any rigorous shaking whatsoever. In less than five minutes, I will get the results of the test. This nitrate test kit is so sensitive that it can detect changes in nitrate levels as low as 0.2ppm.

 

[kilnakorr]

Used Salifert! This kit was so much easier to use with only three steps involved. I do not have to do any rigorous shaking whatsoever. In less than five minutes, I will get the results of the test. This nitrate test kit is so sensitive that it can detect changes in nitrate levels as low as 0.2ppm.

Thanks for the tip.
I forgot about this thread, but my rodi water I used for dilution was contaminated and gave wierd results.
I seem to get consistent results with nyos, but its really expensive so will look elsewhere in the future.