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I'm helping my daughter with a science experiment for school to show the effect of CO2 enrichment on plant growth. We have two small tabletop greenhouses with approximately 10 Liter volume and we're trying to achieve approximately 1500 ppm in one of the greenhouses. Our current idea is to use carbonated water as a CO2 source. Basically, from what I've read typical carbonated water will have about 6 grams of dissolved CO2 per liter which translates to 3 liters of CO2 gas, if I understand correctly:

Carbonation is measured as either ‘volumes’ or grams per litre. One volume means 1 L of CO2 in 1 L of drink. This is equivalent to 1.96 g/L (normally quoted as 2 g/L). A typical carbonated soft drink contains approximately 3–4 volumes (6–8 g/L) CO2.

Assuming the low end of 3 liters CO2 gas per liter soda we get each milliliter of soda contains 0.003 liter CO2. Ambient air has about 400 ppm CO2 or 0.04%, or about 0.0004 liters CO2 per liter air, so to bring it up to about 1500 ppm I would need to add 0.0011 X 10 or 0.011 liters CO2 to the greenhouse, or about 4ml of carbonated water.

The problem is this whole process is very imprecise, and it would be nice if there was a way to measure the CO2 content within 100 ppm with a range of say 0 - 5000 ppm which doesn't cost hundreds of dollars, since this is a 9th grade science project.

Any ideas?

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There are a number of simple sensors around for Arduino/Pi setups that will measure CO2 for around $50 - pubs.acs.org/doi/10.1021/acs.jchemed.8b00473 has an example of their use. There are packaged sensors with displays for similar prices on online marketplaces. some considerably cheaper.

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