Test Kits

[Duz]

I seem to read quite a lot about test kits on this forum. I know most people suggest using the API test kit and that test strips are rubbish. When I got my tank a few years back I brought some test strips to check the water, now I just get the lfs to do it for me. After joining the forum I noticed that the scales for test strips and liquid kits are completely different. While test strips normally go: -

• Nitrate 0 20 40 80 160 200
• Nitrite 0 0.5 1 3 5 10
• etc etc

Liquid test kits do it to a tenth of a decimal (0.1, 0.2, 0.3, etc).

I was just wondering. Why would companies who produce both strips and liquid test kits rate them differently? Surely if they are producing 2 products they wouldn't make 1 test kit completely inaccurate and the other spot on. I understand that they properly want some money but if they had 1 kit completely accurate the other almost useless then economically the inaccurate kits wouldn't be feasible as everyone would notice and they wouldn't buy them (if that makes sense).
Then I thought would it not make sense that the stripes are equivalent to the liquid kits. For instance would Nitrate 20 not be the same as 0.2? Could it be that the scales are in ppm/ppb? I know it properly sounds stupid but I don't quite understand why companies would produce 2 products which are completely different from each other. I agree that liquid test kits will be more accurate but I just don't understand why they would make strips inaccurate.


Then I started reading through the little (well quite large) leaflet, it even says "... nitrites levels should always be 0 ..." and that "for more precise readings use the API test kit" but goes onto say "the API nitrite test kits (liquid test kit) reads from 0-5 ppm (mg/l) in 6 increments: 0, 0.25, 0.5, 1.0, 2.0 and 5.0." Does that not indicate that although the liquid kits are more accurate that the test strips are roughly the same?

Liquid test kit for nitrite 0 0.25 0.5 1.0 2.0 5.0
Strips test kit for nitrite 0 0.50 1.0 3.0 5.0 10.0

This kind of proved me wrong think that liquid test kits and strips used different measurements e.g. ppm/ppb. But I don’t know if that only applies to nitrites or nitrates and ammonia to. Are test strips really as bad as people make out? Mine have always seemed to back up the liquid test kit results and why would 2 companies make 2 products, with 1 being accurate and the other completely inaccurate. Was just wondering if anyone would know.

Edited by Bignose: watch the language please, the word I blocked out was over the top and completely unnecessary for a family-friendly forum.

 

[Bignose]

At least some of the reason is that the chemistry of liquid tests and strips tests are different. Different chemistry means that the color change will be different. The color charts will be marked at the values that the color change is most noticeable, not just where the company wants them to be. In other words, the company is limited by what the chemistry will do.

Another point I like to make is that the error margins for any home test is going to be at least +-5% and maybe as high as +-10%. This is quite simply because the tests are manufactured cheaply and then the human element in the testing also compounds the error. So, any value measured with a liquid or a strip test really says that the true value is in quite a range. Unless you are performing each test in triplicate or more, a wide margin is just part of the testing method.

But, the good news is that most of the time, we don't need to know values really accurately anyway. As in the other thread in this section about test kits, we don't really need to know the pH to +- 0.1 pH units. And, any ammonia or nitrite tells you that something is wrong -- it really isn't a big difference between 0.25 ppm ammonia and 0.50 ppm -- both need to be addressed as soon as possible, really. The exact value may tell you if your level is immediately deadly or not (see: http/www.fishforums.net/index.php?/topic/154313-of-toxic-ammonia-charts/ ), but as I wrote in that link, any amount of ammonia needs to be addressed -- even low levels apparently can cause chronic immune deficiencies. Very similar statements can be said about nitrite -- any non-zero level needs to be addressed sooner rather than later. And the evidence shows that nitrate toxicity really doesn't become an issue for several hundred ppms. Of course, each of these statements may be different for individual species or even individual fish. This is where research into buy before buying becomes important, and knowing your individual fish's normal behaviors so you can spot when they are doing something abnormal.

Overall, though, the point remains the same -- to be successful at this hobby, you actually really don't need to know the exact values of the test results very accurately.

 

[Duz]

Thanks bignose.