modified lung Posted September 3, 2022 Share Posted September 3, 2022 (edited) I recently bought some Aquarium Co-op test strips. A few people on the forum have been having problems with the ammonia strips. I've been a water quality analyst for quite a few years now—previously at a research lab for fish conservation and now at a large network of fish farms. In that time I've done a lot of experimenting with the different test kits I've been provided. So I thought I'd try to figure out why people are having problems with these strips. Before we can gauge their accuracy, we need to know what exactly the ACO ammonia test strips are testing. There are multiple types of ammonia—ammonia (NH3), ammonium (NH4+), and total ammonia (TA or NH3/NH4+) which is the total amount of NH3 and NH4+ combined. NH3 is also often referred to as "unionized ammonia" or "free ammonia" to more clearly differentiate it from the other forms. Some tests only report the nitrogen in ammonia (NH3-N, NH4-N, total ammonia-nitrogen/TAN) but the difference isn't very significant at low levels (1.0 ppm NH3-N = 1.2 ppm NH3). The ACO test strip bottle is labeled "Ammonia Test Strips". If we take the label literally, we might believe the strips test for NH3. However, this is hard to trust because many test kits, especially for the aquarium hobby, aren't very clear about what exactly is being tested. Turning the label around, NH3 would not make sense with the color scale given on the back of the label. For example, I would think the "caution" level for NH3 would be considered closer to 0.02 ppm which is far lower than the 0.5 listed on the label. Not to mention 0.5 ppm NH3 would kill many fish in a couple days which I personally would label as "change water" instead. Here's the ACO ammonia strip color chart next to an example of a NH3 color chart that does make sense: However, the ACO color chart does make sense if the strips are instead testing for TA or for NH4+. For reference, the API ammonia liquid test kit measures TA. And the API color chart is very similar to the ACO chart. How Different Types of Test Strips Work If you're not interested in how ammonia test strips work, feel free to skip to the "Experiment" section of this post. Generally, test strips that measure TA or TAN have two pads. Notice the front labels of both these test strips say "ammonia". However, the back label of the HACH Aquachek ammonia strips specify that TAN is being tested while the ACO back label still only says "ammonia" (HACH is a company that makes highly accurate, scientific grade water quality test kits) Here's a photo of HACH ammonia test strips next to the ACO ammonia test strips: A lot of people here already know that the amount of NH3 and NH4+ in a water sample depends on the pH. Higher pH means more NH3. Lower pH means more NH4+. The large pad on the HACH strip increases the pH of the water sample to 10 in order to convert all of the NH4+ to NH3. The small pad then measures the NH3. To work properly this requires the water sample to be a specific volume. In this case the HACH instructions specify that each water sample should only be 3 milliliter or the result may not be accurate. The API liquid ammonia test kit works in a very similar way. The bottle #1 reagent increases the pH and the bottle #2 reagent measures the NH3. ACO strip instructions don't mention a specific volume of water is necessary. In fact, videos made by ACO themselves show their strips being dipped into a 1 or 2 liter container of water and even straight into a large-ish fish tank. This would mean no pH change is required for the strips to work. I confirmed the HACH strip alters the pH by placing a whole strip into some 7.0 pH calibration solution and measuring the pH increase. The pH only rose to 8.0 because the volume of calibration solution was more than 3 milliliters. I did the same with an ACO strip and no change in pH was observed. But ACO strips don't need to change the pH if they were meant to measure only either NH3 or NH4+. This is only necessary if the strips are meant to measure TA. Taking all of this into consideration, I'm guessing the ACO ammonia strips are actually testing for NH4+. This would make a lot of sense because the strip might only need one pad and in most normal cases NH4+ is close enough to TA to use the same color charts. Experiment First, I tested a sample using both a HACH Aquachek ammonia strips and a HACH liquid test vial read with a HACH spectrometer. For test strips (and liquid tests as well), keep in mind the results rarely look exactly like the color charts because of a number of factors that influence the speed and intensity of the color change. Temperature and light are two examples. This means, if you want a high degree of accuracy, you have to develop an eye for interpreting the results with your testing conditions and habits. Of course this isn't easy unless you have tests from known concentrations to compare with your results. But for knowing if your aquarium is in a safe general range, this isn't terribly necessary. In developing an eye for HACH strips I've learned to pay more attention to the amount of yellow that fades than the shade of green that develops. I would interpret my HACH strip results as 0.8 or 0.9 ppm TAN. The liquid test vial and spectrometer showed 1.16 ppm TAN. Close enough for a strip. Next, I took part of the water sample and some baking soda until the pH rose to 8.1 just to see if there will be any noticeable difference. Lastly, I took another part of the original sample and added enough ammonium chloride to bring the TAN up to about 200 ppm. Unfortunately, I don't have a test that can measure such a high amount of TA. But we shouldn't need to because all we need to see with this sample is if the strip results read within the range of the kits or off the charts. Here are the possible results we should expect depending on what the ACO strips are measuring (the amount of NH4+ is a little higher than the TA because of the extra H compared to NH3): Original + Baking Soda + Ammonium Chloride pH 7.3 8.1 7.3 TAN 1.2 ppm 1.2 ppm ~200 ppm TA 1.4 ppm 1.4 ppm ~240 ppm NH3 0.02 ppm 0.10 ppm ~2.7 ppm NH4+ 1.5 ppm 1.4 ppm ~255 ppm Results Here are the ACO test results for for the original water sample (left) and the sample brought to pH 8.1 (right). The two results look almost the same: 0.5 ppm: This might look like an unexpected result but we should first know that all water quality tests have a range of accuracy. For ammonia tests that range is usually above 0.25 ppm. That means to the human eye even trace amounts of ammonia will look almost exactly like 0.25 ppm on the color chart. For example, in the past I've compared the results from the API liquid ammonia test kit with HACH liquid test vials read with a spectrometer. I found that even readings around 0.02 ppm TA with the liquid vials and spectrometer looked exactly like 0.25 ppm TA on the API color chart. But given that 0.5 ppm is the next color after 0 ppm on the ACO ammonia strip color chart, the range of accuracy for this test is probably above 0.5 ppm instead of 0.25 ppm. That means these do show one of the possible expected results: between 0 and 0.5 ppm. But that's not all. I said they "almost" look the same. Notice the more yellow ring around the edges of the pad on the right? On some strips that means a slightly lower concentration was measured. Although, I haven't used the ACO strips for long enough to be certain if this is the case here. Either way, these results don't make sense if the ACO strips are measuring TA or NH4+. They would, however, make sense if the strips were measuring only NH3. Here are the results of the sample + ammonia chloride with the HACH and ACO strips: As you can see the HACH strips read off the charts which is expected if they measure TAN. The ACO strip reads I'd say somewhere around 2.0 or 3.0 ppm. The ACO strips again line up with the expected NH3. But that's not all. Interestingly, when using an ACO strip on a 3 milliliter water sample that was already tested by a HACH strip, the ACO results showed the correct amount of TA (1.2 ppm) instead. Remember, the large pad on the HACH strip increases the pH to 10 in order to convert all of the TA to NH3. My pH meter isn't small enough to fit into 3 milliliter so I couldn't confirm the pH was at 10. But I was able to confirm the large pads do increase pH in a larger volume sample, so I trust the HACH strips work as described. Here's a picture of another ACO strip used on the original sample (left) next the a strip used on a sample exposed to a large HACH pH altering pad: Conclusion That's at least 3 points of evidence that ACO ammonia test strips only measures unionized ammonia (NH3). Each part of the experiment I described above was repeated at least 3 times with water from 3 different sources each with 3 different concentrations of TA. The results all lined up with ACO strips measuring NH3 …and very accurately I might add. I was easily able to distinguish between 0.8 and 1.2 ppm. Far, far more easily than with the expensive HACH strips. That's extremely impressive. And extremely useful for applications where NH3 doesn't need to be so low. So this might not be such a big deal …the Seachem Ammonia Alert cards only measure NH3 for example. But the Seachem cards have a color chart that makes sense for the typical levels of NH3 that might be found in an aquarium …while the ACO ammonia strips do not. Unfortunately, that makes the ACO ammonia strips not very useful for most aquarium applications, especially if the range of accuracy is indeed above 0.5 ppm. Edit: I've confirmed the range of accuracy seems to be above 0.5 ppm NH3. In testing my blackwater tank with a pH of 5.5, the ACO strip showed 0.5 while other tests including TA tests showed 0. Although the ACO pad did again have the yellow ring around the edges that I mentioned earlier. (For reference, at pH 5.5 there would only be 0.0002 ppm NH3 for every 1.0 ppm TA.) ---------------- This is kind of awkward. It seems a lot of people on here have had problems with the ACO ammonia strips. I was hoping if I bought some, I could find what was being done wrong. But I think people are in fact using them correctly. The strips are just measuring something very different (NH3) than what I think is reasonable for them to believe (TA). I mentioned these are still useful for some applications. I plan on using them for my many greenwater cultures. I sometimes add high amounts of NH3 to them. I've been looking for a quick, cheap way to test if the greenwater has consumed enough NH3 to be safely dumped into my other live feed cultures (daphnia, moina, etc.). These ACO ammonia test strips will work great for this, especially since they can be cut in half without affecting their accuracy. Edited September 4, 2022 by modified lung New paragraph near end 6 4 2 Link to comment Share on other sites More sharing options...
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