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Educational colorimeter kit's video poster

Kit for making a programmable colorimeter for analytical chemistry and biochemistry labs & activities. Arduino compatible. Read more

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This project was successfully funded on June 1, 2012.

Kit for making a programmable colorimeter for analytical chemistry and biochemistry labs & activities. Arduino compatible.

Using the colorimeter to test water in an aquarium and an educational application !

This update is also a new blog entry posted by Jo Long to the colorimeter project.

As an aquarium hobbyist (currently enjoying 3 freshwater tanks), I have been using the colorimeter to measure the quality of water in my aquarium tanks. I like the API test kits - they are very easy to use, cheap and reliable. The color of the test is compared to a chart to determine the ppm of the nutrient.

However, this method does not have great resolution, especially at the higher concentrations. For example, while nitrite is pretty obviously 0ppm, we can only determine that ammonia is approximately 0.50 ppm and nitrate is somewhere in the range of 80-160 ppm. With the colorimeter I can get a more accurate readings by measuring absorbance of red light (ammonia) or green light (nitrite and nitrate) and calculating concentration using the colorimeter software. A comparison of the two methods in shown below:

  • Ammonia - 0.50 ppm (chart);  0.47 ppm (colorimeter)
  • Nitrite - 0.00 ppm (chart); 0.00 ppm (colorimeter)
  • Nitrate - 80-160 ppm (chart); 111.75 ppm (colorimeter)

Quantitative measurements of aquatic nutrients are extremely useful in any number of biology labs. For example, investigating the rate at which ammonia is converted to nitrate by aquatic nitrifying bacteria, and how activity of these microbes is affected by environmental parameters (dissolved oxygen, temperature, pH, light).  This is a pretty fun and engaging lab which students can easily carry out in a classroom with only a few additional supplies. As well as the colorimeter and API test kits, you will need a stock of ammonia, some beakers and a source of nitrifying bacteria. I have personally tried several commercially available solutions containing nitrification bacteria, and found nothing works quite as well as taking some gravel from a well-established aquarium tank. Simply scoop out some gravel, gently rinse and place in a beaker containing 2-3 ppm ammonia in tap water. Do not use distilled water as the bacteria require phosphates and this is not present in distilled water. Take a baseline measurement of ammonia and nitrate at the beginning of the experiment (Day 0), and then measure levels again every 24 hours over a 4 day period. The actual measurements do not take too long and can easily be completed in a class period. I would recommend taking triplicate measurements and taking the mean ppm value.

In the graph below I have shown some sample data showing the levels of ammonia and nitrate over a 4-day time period. The data labelled "substrate" represents the beaker with gravel (and nitrification bacteria) from an established aquarium, and "control" data represents a beaker with no bacteria from the aquarium. As you can see from the data, levels of ammonia had almost disappeared after 4 days with significantly more nitrate compared to the control. Levels of nitrate did not change much in the control experiment.