Comparing Tetra test strips and the API master kit

[Kat_Rigel]

I know I know, Cory has done a video on this. But I am a numbers and charts person, so I wanted to offer some more data on this topic. I have a background in chemistry and I know a lot of you NERMS on here like this sort of detailed analysis, so here it goes.

Once I saw the video, I thought it was genius! Of course! If you are in the ballpark, much better to use those quick test strips (which you will use more often than the liquid kit because they are so easy. As a reminder, you can see Cory's video here: 

 

Because I thought this was great info, I went out and bought some test strips to compliment my API test kit. Of course, like any info on the internet, I also wanted to test it. I did a quick test a few weeks ago and got very different results. Whoa! That's weird, and not what Cory's video showed! So today I sat down and did some more precise testing/recording numbers.

For this experiment, we have to accept that the human eye just sucks at interpreting color accurately. If we wanted to get super precise numbers, we would want something like a spectrometer, but that's not financially realistic for the average person. (Doesn't mean I'm not looking 'em up on ebay after this...)

I have two different tanks I tested this on, but only once each time. One is a planted 60 gallon community tank and the other is a 10 gallon snail tank. I try to keep the gH higher in the snail tank for shell health, so that measurement is particularly important. Both tanks are moderately/heavily planted. The snail tank is overstocked, but I'm pretty diligent about water changes. The Community tank is a little understocked, and please note that I administered some General Cure today to deworm, so that could potentially interfere with results.

When I did the test, I had to break my bad habit of not shaking the API test kit for a full minute. You can categorize this under "I am smarter than the sum knowledge of all fishkeepers." arrogance. Surely, not shaking for a full minute couldn't make that big a difference, right? Well, I can get into my previous quick and dirty results, but yes, you need to shake for the full minute. I got very different nitrate results when doing this. Anyway, you can't test the API kit if you aren't going to use it according to the instructions. Please note that I DID NOT USE THE API TEST KIT FOR pH. I have a pH meter which I consider to be the most accurate option available, therefore I compared the test strip to the API kit on nitrate, nitrite, gH and kH.

You can see the results below in chart and list form:

OK, so what are we seeing? Well first we're seeing that my nitrate levels in my tank are WAY high and I need to fix it, but that's for another day.

Within the community tank, everything is pretty much the same between Tetra and API. This is consistent with Cory's results.
Now if we look at the Snail tank, we see some variation. Ph and nitrite are looking the same, but gH, kH, and most concerningly nitrate are showing differences. The difference in nitrate could be because of the logarithmic scale it uses to refer to color. Ever notice how the measurement chart jumps from 0, to 5, to 10, then 20, then 40, etc? It's a bigger and bigger difference with each color change on the chart. So if you have a very high concentration that you are reading, and you're having trouble reading it, your mistake matters more than if you were reading something closer to 5. (Ex. Is it 5 or 10? Eh, it's close. Is it 40 or 80? Whoa, big difference!) I did have trouble figuring out the color of the nitrate on the API test kit; I have included pictures of the results here so that others can give input, if you like. Please note that because I thought the API nitrate reading was between 40 and 80 ppm, I split the difference and called it 60ppm.
I have no explanation for the difference in KH and GH readings.

API results for Snail tank:

Tetra test strip Snail tank results:

 

OK so what does all of this mean? I think it means that if your tank is generally healthy and you are just doing regular water checks (once a week, once a month, etc) and you want a heads up on anything that might be an issue, you're probably ok using the Tetra test strips. But if you are having issues with something, you may want to try the API kit. BUT, I would argue that we don't really know which method is more accurate. Within the fish community, we sing the praises of the accuracy of the API Master test kit. But why? What are we comparing it to? Well, we have reports of the test strips going bad very easily, so that's one reason. But ideally, I would want to measure my water parameters with a mass spectrometer (this is me being a super nerd- it is a scientific instrument which gives you VERY accurate reports of concentration. Again, not realistic for the home hobbyist at all! But has anyone every tried it? Ever? Anywhere? I expect API did the testing, but those aren't exactly easy to look up. Why do we choose API as the best? I think it's worth considering.

 

Tl;dr The API Master test kit has fairly similar results to the Tetra strips if you are measuring low concentrations (everything in your tank is going as expected,) but there can be major differences if you have something like nitrates very high. This is because it's tough for the human eye to read colors accurately. I have no explanation for the differences in kH and gH in one tank but not the other. Also, consider that we don't necessarily know that the API Master kit is the most accurate. Everyone says it is, but what are we comparing it to?

Thanks for coming to my TED talk. lol I don't work as a chemist anymore so sometimes it's just nice to get this out of my system. I hope some folks find this helpful/interesting.

[ChemBob]

Very interesting! I recently got Tetra test strips to quickly check nitrates on a new tank I'm cycling using the plant method so I know I'm fertilizing enough. I am about 99% sure I heard @Bob say he uses them on one of his recent streams. 

Edited October 20, 2020 by ChemBob

[demicent]

Thanks for your in-depth post.  I use the API kits and Tetra Easy Strips.  I am cycling four new tanks, 3 planted and 1 planted with snails.

I keep meticulous records because I'm a geeky  nerm and I can't trust my memory anymore.  When I use the strips, it's to do a check to see if the parameters are trending up or down.  The actual numbers are not as important, it's to show movement in the values that might need my attention.  I do a quick dip on all four tanks and check the results against the previous readings.  I use the API kits more sparingly and tend to base my actual numbers on them, mainly because "the internet" says they are more accurate and I have no way to know.  In the end, I am hoping for consistent results that remain toward center of the "good" parameters and I probably shouldn't obsess over wanting to know the actual numbers.

With only two weeks of data, my test strips and API kits are not producing close results, part of that may be me needing to train my eye to interpret the colors.  I use a pipette to get as close as possible to 5 ml.  

When I was in kindergarten, the teacher asked us to draw a picture of what we wanted to be when we grew up.  I drew a scientist working with test tubes.  Between the aquariums and my miniature rose hobby, my dream has kinda sorta come true.

Again, thanks for your thoughtful work on this topic.