I made a 40 ppm Nitrate calibration solution last nite, since there was a 40ppm color box on my nitrate test card:
Here's what I did:
- 1g of KNO3 in 500ml of distilled water which makes 2000ppm nitrate solution
- 10ml of this 2000ppm solution mixed with 490ml of distilled water produces 40ppm nitrate solution
Personally, I had a rough time telling the difference between the 20ppm and 40ppm color boxes on my card when compared with my 40ppm solution. So, I diluted my 40ppm to 10ppm by mixing the 40ppm 1 part to 3 parts distilled water. The 10ppm color box is much easier to match and I feel the color was almost a perfect match. I think that API did a good job on this particular nitrate test kit for me. At least it should be close enough for what I am doing.
Last edited by tedr108; 03-27-2008 at 05:19 PM.
Cool. I'll have to try that. What does API stand for? Aquarium Pharmaceuticals Institute?
Yes, you are right about API.
Now an accuracy of +/- 20ppm?
Now EI can hit that pretty easily.
This is why I switched to Dry dosing about 10 years ago, no one would make DYI calibration solutions for NO3, K, PO4 etc, and no one would buy a 60$ Lamotte kit.
BTW, you can dilute the sample into the range that is better for any test kit kit also.
Say it(the test kit) is best in the 5-10ppm color range, then dilute: 1part sample to 5 parts DI water etc.
Diluting the sample aquarium water to help in matching my nitrate test color card is an excellent idea, Tom. Thanks.
Once you have a set up ref solutions, you can easily see how poor the test kits are and the inherent problem.
You might get lucky and get one that is actually "accurate".
But not everyone else is so lucky......so some will run around telling everyone that all API test kits or whatever brands are accurate and fine.
It's not safe to assume that however. You need to consider the sampling(1 or 2 in most cases), no better than coin flipping
Or the folks that never use more than a single point ref solution and then only 1-2x to see.
Unless you find a problem, you will not see much of a need and be over confident about your test and the method to evaluate it. It very well might be the case that it is not an issue for you personally, but for others and the folks you do give advice to, it may be.
Like aquariums, each test kit is slightly, sometimes radically different.
Generally, even folks that test NO3 weekly etc, rarely calibrate much after 1-2x, or with each new test kit they get. Test kit reagents expire, who knows how long they sit on the shelf at the LFS.
You can get around some of this by measuring frozen water samples(Taken weekly etc) all at once and doing the test all at once along with calibration.
This way everything is the same.
The trade off is that you do not get to adjust and change as go with the dosing etc. You only get to see the final trend over time.