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NO3 Calibration Results


New Member
14 Feb 2009
I thought i'd convey my results following an evening of measuring small amounts of liquid and dripping tiny bottles.
I decided to 'calibrate' my NO3 test kit for two reasons:
1. I have a mistrust in things that are 'cheap' i.e. not £100's
2. I must be colour blind because I can't tell if I have 10ppm or 100ppm in my tank
I am using a Nutrafin Multi Test Kit (liquid)

So, using the method for creating NO3 reference solutions posted on the barrreport forum I made a series of solutions with DI water (from halfords) and KNO3 powder. Unfortunately I only have 3 test tubes so my comparision was limited. Firstly then, i'll note what my eye read the standard solutions as:

20ppm standard reads approx. 2ppm (i.e. < 5ppm)
30ppm standard reads approx. 20ppm
40ppm standard reads approx. 50-60ppm (cant tell) - i think my eyes must have gone funny at this point
50ppm standard reads approx. 30ppm
100ppm standard reads approx. 60-70ppm (again cant really tell)

Then tested my tank water (on chart and in comparision to some of the above standards)
1st time it read from chart 50-100ppm
2nd time it read from chart 30-40ppm - this shows how bad my eyes are with different shades of purple!!
Also tried it in comparison to 50ppm std and 100ppm std, it was inbetween the two lying closer to 50ppm standard.

Thus, my conclusions.
- This kit appears to read 10-20ppm lower than actual value (ignoring one anomaly -sp?)
- My tank water would appear to be about 60ppm based on comparison and by applying 20 in addition to read value of 30-40
- I can only see purple now!!

- Firstly does this even matter? A lot of people do not use test kits and rely on water changes regularly to reduce NO3. I tested my tap water a while ago and it was the same colour purple as the tested tank water, so im concerned my 50% weekly is doing nothing to help reduce NO3.
- How are my fish not dead if NO3 is 60ppm? Is there not a limit as such? Is it harmful in the long run at, especially with the plan to add some Pterophyllum scalare soon.
- I was initially dosing KNO3 as part of EI routine, stopped for a while then carried on so as not to cause K deficiency (only using KH2PO4 otherwise), but consequently increasing already high NO3. Do i perhaps need to change KNO3 to KSO4 for my K?

Hopefully someone may be able to give me a little guidance on this issue and may encourage others to give 'test kit calibration' a go.

To be completely honest, test kits are probably going straight in the bin when the drop checker arrives because if im not getting an accurate result I might aswell not know the result!

Thanks for reading, sorry it was long. Cheers,



19 Jul 2007
Lincoln UK
Of course it does matter how much nitrate is in your tank water but the limits are not in the 60s they are in the 100s if not more. Tom Barr has tested up to 140ppm before shrimp deaths as far as I know. Not sure how far above this he has tested.

Your tap water versus tank water comparison shows how far out the colour depiction to the human eye is!!! There is no way that your tap water is 60ppm!!! It will be 20ppm I would've thought at the very most. Therefore this makes your tank water reading suspect too even with the calibration method!!!

You can try the K2SO4 instead of KNO3 andse if you get defficiencies. This is assuming that you are free of defficiencies already. You would need to leave it for 3 or 4 weeks and see if there are defficiencies and with N being such a needed nutrient the result should be pretty visible.

I wonder why you were worrying though. How long have you followed this dosing regime and have you had problems with the fish? If you have been running it a long time and your tap water (in theory) was 60ppm on top of dosing then you would have seen problems I think :)

I don't test and haven't for a long long time. I live in agricultural country here in Lincolnshire where N and P are pretty high in the taps but we're not talking 60ppm. I haven't tested but the maximum allowed in this country is 50ppm. In the US they state 10ppm. The average recorded last year according to my water company reports was 13.8ppm.

According to Portsmouth water the averages in your area are quite suprisingly in th 30ppm region but most definately not 60ppm. Here is their page. Click on your area to find out their figures:
http://www.portsmouthwater.co.uk/about- ... spx?id=152



Expert/Global Moderator
11 Jul 2007
Chicago, USA
A couple of comments along the lines of SuperColey1's response:

1. Would the evening have been more fun sipping a glass of Sauvignon Blanc while watch your tank rather than getting crosseyed checking out the color purple?

2. I actually have been dosing 60ppm NO3 for the better part of a decade and have not experienced any short term or long term negative effects. This shows that high NO3 is not really a problem.

3. The purpose of your water change is really not related to avoidance of NO3 buildup. The water changes are for avoiding organic waste buildup which contributes to algal blooms and does have toxicity ramifications.

4. Your observation that many folks avoid testing and that your fish thrive regardless of test kit readings should be a welcome indication that hobby grade test kits are thoroughly useless. :idea:



6 Jul 2007
Aston, Oxfordshire
Nice one for taking the time to do this and to share the results. Your suggestion of binning the test kits sounds good, is there anyway of us all meeting up and burning our test kits in one giant sacrificial fire? Well the box and manual at elast if not the liquids (prob not a great idea! :lol:)



New Member
Thread starter
14 Feb 2009
Thanks for all of you replies. I think the calibration was just something I had to give a go, to see what would happen.
You have all cleared up my main worry which was that high NO3 would be harming my fish. I have not seen any problems with them but felt it might be something which doesn't show...they just die suddenly. Now I know not to worry too much about sub 100ppm.

In terms of NO3 for the plants. I haven't been doing the dosing regime long enough to make any conclusions about deficiencies but I know that they can cause problems. So i think my plan of action is just to carry on with the regime (which was the standard EI scheme from tom barr for a 20-40Gal tank) and continue 50% weekly WC and not worry about changing from KNO3 to K2SO4. The only thing I could do is mix my ferts in DI water so its only the measured amount of NO3 being added that goes into the tank, but then if my tank water is from the tap anyway then theres not really much point.

All in all, great stuff. I'll just keep an eye on things and get the test kit out again bi-weekly/ if I note any significant changes. Now just to steady the CO2.....

Thanks guys! :D


2 Aug 2007
I'm just glad you claibrated the test kit and showed others that they are not always correct as often claimed on line.

Tom Barr

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