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.
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.
- 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.