Accuracy of Sera Nitrate test kit

[PeterGwee]

Like to have the opinions of Sera Nitrate test kit users as to whether the test kit is accurate? (Due to the fact my nitrate climbs occasionally at alarming rates even though bio-load seems moderate and feeding is minimum). Any experiences with other brands of nitrate test kit and the accuracy of the kit is welcome also.

[bclee]

One easy way to test your kits is to us it on solutions of different known concentration.

You can easily make up solutons with KNO3 and dilute it to the desired concentration.

BTW, are you using root tabs with N? I find those stuff raise the NO3 level pretty fast.

BC

[PeterGwee]

Well, I did that just half and hour ago...Here is the method and finding.

(To test what the kit would register at 1.72ppm of nitrate)
1) 0.125 of a Tsp of KNO3 to 500ml of tap water.
2) 1ml of the mix 500ml to another 500ml of tap water.
3) 20ml of the final KNO3 mix to test.
4) Colour shows very close to 5ppm (Hard to tell but it shows almost exactly the same colour as 5ppm on the colour chart.)

(To test what the kit would register at 5.15ppm of nitrate)
1) 0.375 of a Tsp of KNO3 to 500ml of tap water.
2) 1ml of the mix 500ml to another 500ml of tap water.
3) 20ml of the final KNO3 mix to test.
4) Colour shows is exactly 5ppm on the colour chart.

Conclusion = It seems that the kit would round off the result to the intervals indicated on the colour chart. (1.72ppm of NO3 indicates 5ppm on colour chart and so does 5.15ppm????)

Well BC, my nitrate now seems to be under control except that I took Tom Barr's advice and forget about the results I got from the kit as he feels it is not accurate and dose 10ppm of KNO3 2X per week. The kit currently shows 20+ ppm of nitrate in my tank..guess I overdose NO3 liao..[]

[budak]

peter,

please continue to post your observations following dose (or overdose) of KNO3. I am seriously thinking of starting too, in place of K2SO4.

[PeterGwee]

Erm..budak..I don't think you want to use KNO3 to boost your K up to 20-30ppm are you? If you do that, your NO3 would be way too high! I am actually dosing to keep about 5-10ppm but the test kit is not that accurate according to Tom Barr (I cannot see any consumption of NO3 during the week?)

pH= 6.5
KH= 3
NO3= 20+ ppm but under 30ppm (Might not be accurate)
PO4= 0.5 (Might not be accurate..Mmmm..might be even be at 0.1 or less!)
GH= 5
Traces = TMG at 3.8ml per week (underdosing..might up it to 2X per week)

[bclee]

----------------
On 3/13/2003 9:19:38 PM

(To test what the kit would register at 1.72ppm of nitrate)
1) 0.125 of a Tsp of KNO3 to 500ml of tap water.
2) 1ml of the mix 500ml to another 500ml of tap water.
3) 20ml of the final KNO3 mix to test.
4) Colour shows very close to 5ppm (Hard to tell but it shows almost exactly the same colour as 5ppm on the colour chart.)

(To test what the kit would register at 5.15ppm of nitrate)
1) 0.375 of a Tsp of KNO3 to 500ml of tap water.
2) 1ml of the mix 500ml to another 500ml of tap water.
3) 20ml of the final KNO3 mix to test.
4) Colour shows is exactly 5ppm on the colour chart.

Conclusion = It seems that the kit would round off the result to the intervals indicated on the colour chart. (1.72ppm of NO3 indicates 5ppm on colour chart and so does 5.15ppm????)
----------------

Peter, don't forget about the NO3 in the taps. There should be slight NO3 level in the tap water.

I used to use Watson's distilled drinking water for dilution.

BC

[geoffrey]

Gwee,

I personally have the same problem differentiating the colours myself, particular at night under flourscent light. Try doing it during the daytime, seem easier to differentiate for me.

You will notice the resolution between 10 to 20ppm is wider compared to the lower range of 0 to 5ppm, 5 to 10ppm. I had 20ppm of NO3 before and noticed the colour changed very quickly to the deeper colour but as I lowered the NO3 (now at 10ppm), I noticed the time needed for the colour change seem shorter (Wondering whether anyone share the same observation). So, I used time as an approximation for readings between 10 and 20ppm.

I have no problems lowering NO3 from my high of 20ppm to 10ppm. I did it thru 50% water change twice weekly and reduced total weekly dosage of KNO3 by half. Besides that, I also up my CO2. It has since equilibrate at 10ppm.

[PeterGwee]

Thanks geoffrey for the feedback... I did another test after comments given by BC that the tap water might contain some nitrate (might be 0.5ppm as the test kit did not detect any when I test for it). The following is the observation found.

(To test for 10.51ppm of nitrate using Newater)

1)Added 0.375 tsp of KNO3 to 350ml of Newater.
2)Add 1ml of the mixed NO3 solution to another 350ml of Newater.
3)Draw 20ml of final mix sample to test using the Sera Test kit.
4)Found the result shows 10ppm exactly....(Mmmmm...well at least it is quite close but hard to detect small shift in nitrate..especially consumption by plants.)

Anybody care to write to Sera to ask if the time taken for the testing is important? How about the amount of powder regent used as well...will the amount affect the final result?

Also..did anybody wrote to PUB to ask for a detail analysis of the current tap water quality? Ermm...like a breakdown of nutrients..NO3, PO4, Mg, Ca..and etc.. ...Me tried writing but seems to be no reply..The current one shown on their side is too general to my liking..Imagine NO3 ..0.5-15ppm...[]

[bclee]

The powder reagent is a reducing agent, Cadmium if I'm not wrong. The test is done by reducing the NO3 with the reducing agent. The prescribed amount should be in excess for reducing the NO3 ppm range that you are testing for. Therefore, the quantity of the reagent should not be so critical.

BC

[dettol]

Hi Peter and all, found PUB's site
Hope its useful.
Pub