Nitrate Testing - Red Sea Kit

[member 99594]

Hey all,

Just have a quick question for those who use the Red Sea Nitrate test kit.

My tank is about six months old. I have been testing nitrates, phosphates, alkalinity and calcium magnesium. My nitrates are usually under 4. Typically was getting 1s and 2s. However, recently they’ve started to climb due to the tank being more mature and adding more fish etc.

The other day nitrates tested about 12. I did two fairly large water changes and tested again. This time they came back at 4. When you test with the Red Sea and you get 4 there is a high range test that you can use. So, I did the high range test and it came back confirming 4.

This got me thinking, should I just be doing the high range test to begin with instead of wasting a test on the lower range? Since really all I care about is that the nitrates are below 5 and they certainly are not going to be 0 when I have live stock and coral.

Thoughts?

Cheers and thanks in advance!!

 

[RL6723]

Hey all,

Just have a quick question for those who use the Red Sea Nitrate test kit.

My tank is about six months old. I have been testing nitrates, phosphates, alkalinity and calcium magnesium. My nitrates are usually under 4. Typically was getting 1s and 2s. However, recently they’ve started to climb due to the tank being more mature and adding more fish etc.

The other day nitrates tested about 12. I did two fairly large water changes and tested again. This time they came back at 4. When you test with the Red Sea and you get 4 there is a high range test that you can use. So, I did the high range test and it came back confirming 4.

This got me thinking, should I just be doing the high range test to begin with instead of wasting a test on the lower range? Since really all I care about is that the nitrates are below 5 and they certainly are not going to be 0 when I have live stock and coral.

Thoughts?

Cheers and thanks in advance!!

I use the Red Sea Nitrate test as well, and I always run the high range test. The only time I have ran the low range test was when I felt like I bottomed out my nitrates. As long as there is still slight coloring on the High range I call it good

 

[member 99594]

I use the Red Sea Nitrate test as well, and I always run the high range test. The only time I have ran the low range test was when I felt like I bottomed out my nitrates. As long as there is still slight coloring on the High range I call it good

Thanks rl

 

[Potatohead]

You can run any divisor of 16 you want basically. I almost always use 4 ml tank water and 12 ml RO and then multiply the result by four. Sometimes 8/8 and multiply by two

 

[jrill]

Something I've been wondering about. Let's say you run the low range and it's over 4. Can you take 1ml of that test colored water, dilute it with 15ml of and read that as your high? It looks about right.

 

[sghera64]

Something I've been wondering about. Let's say you run the low range and it's over 4. Can you take 1ml of that test colored water, dilute it with 15ml of and read that as your high? It looks about right.

When mine is over 4ppm, I remove 8mL and add back 8 mL of RODI water, then multiply the result by 2. Sometimes I have to repeat that process of removing and replacing 8mL again to get the reading below 4ppm (then I have to multiply by 4).

BTW, I am using the Red Sea Pro kit. Not sure if there is a difference.

 

[o00brandon00o]

Something I've been wondering about. Let's say you run the low range and it's over 4. Can you take 1ml of that test colored water, dilute it with 15ml of and read that as your high? It looks about right.

Bump, @jrill Great question, never thought of it like that. I always just ran it again. Interested in what the community says. ;Woot

 

[Dan_P]

Something I've been wondering about. Let's say you run the low range and it's over 4. Can you take 1ml of that test colored water, dilute it with 15ml of and read that as your high? It looks about right.

This approach will not provide meaningful results. You can only dilute the sample water not the test solution.

 

[jrill]

This approach will not provide meaningful results. You can only dilute the sample water not the test solution.

Good to know. Thanks.

 

[sghera64]

This approach will not provide meaningful results. You can only dilute the sample water not the test solution.

Is this true? How do you know?

 

[member 99594]

Is this true. How do you know.

Think of it this way, complete a test with half the solution.

If you were to put half the test solution in the test water your result would be much lower.

 

[link81]

I bet it would work fine. Assuming that your RO water has 0 nitrates (which it should)
run it side by side, do an 8/8 test and a 16 test. take the 16 test and remove 8, and add 8RO and i bet they're nearly the same color. (or at least within sample variation)

 

[sghera64]

Think of it this way, complete a test with half the solution.

If you were to put half the test solution in the test water your result would be much lower.

Ummmmm if we are removing 1/2 the tested solution and QSing back up to “full” with RODI water, the color intensity would be 1/2. It’s just the Beers-Lambert’s Law, right? We keep path length the same and cut intensity in half.

 

[sghera64]

I bet it would work fine. Assuming that your RO water has 0 nitrates (which it should)
run it side by side, do an 8/8 test and a 16 test. take the 16 test and remove 8, and add 8RO and i bet they're nearly the same color. (or at least within sample variation)

That’s what I did a long time ago and it seemed to check out. I’ve done this on my Hanna checkers too (made a calibration curve) and it worked there too.

 

[Dan_P]

Is this true? How do you know?

The color that develops during the test is linearly proportional to amount of nitrate present up to a point, beyond which the color intensity deviates from a linear relationship. When a test sample that is out of range (the nitrate is too high) is diluted, the resultant color intensity cannot be equivalent to the test being run with a diluted sample.

 

[Dan_P]

Ummmmm if we are removing 1/2 the tested solution and QSing back up to “full” with RODI water, the color intensity would be 1/2. It’s just the Beers-Lambert’s Law, right? We keep path length the same and cut intensity in half.

You are making the assumption that the color intensity is linear with nitrate concentration over a very large range which it is not.

 

[Dan_P]

That’s what I did a long time ago and it seemed to check out. I’ve done this on my Hanna checkers too (made a calibration curve) and it worked there too.

It would be helpful to post your calibration curve.

 

[sghera64]

The color that develops during the test is linearly proportional to amount of nitrate present up to a point, beyond which the color intensity deviates from a linear relationship. When a test sample that is out of range (the nitrate is too high) is diluted, the resultant color intensity cannot be equivalent to the test being run with a diluted sample.

Ah, now that makes sense. So clearly diluting the sample before analysis, such that the resultant color is within range, is the way to go.

 

[sghera64]

It would be helpful to post your calibration curve.

Yeah, it was a quick “check” regarding nitrate with a Red Sea Pro. If my memory is correct, the actual reading when I diluted the sample 4:1 was 4ppm (so sample was 16 ppm NO3). That was my “check” against the initial run where it was so dark, that I diluted the reacted sample 2:1 and then 2:1 again - which was between 2 and 4 ppm, but closer to 4 so I called it 4.

With the Hanna checker, I might be able to find that data as it was part of an intern’s project. He was using the checker as a poor man’s spectrophotometer with methylene blue and also molasses (carbon regeneration experiments). Again, if my memory is right, there were upper limits to the linearity on both of those.