I think you are doing this really great project from the Science Buddies website:http://www.sciencebuddies.org/science-f ... #materials
Sunmoonstars and Sarah have given you some excellent sources for background information. It's very important to start a project by learning as much as you can about your subject. You had asked some specific questions about Daphnia in your first post, and I think you should be able to answer all of the questions by now. Is there any question that you didn't find an answer for?
Here is some additional information that will help you be successful with this project.
You should order the Daphnia magna from Carolina Biologicals right away to you can establish a culture to use as a source of baby Daphnia to start your experiment. Daphnia multiply really fast with food and when incubated at the optimum temperature, but you will need lots of Daphnia for your experiment. You will need to visit your local aquarium store to obtain the chemical needed to neutralize chloramine T, if this is used in your local water supply. I recommend also getting a small fine net so you can capture and transfer Daphnia easily.
You need to practice handling and counting Daphnia for the experiment. They are small and swim really fast. The experimental protocol recommends adding 30-50 Daphnia to each water sample, however, I think you will find it difficult to count 30 rapidly swimming Daphnia in one container. I recommend having multiple containers and adding 10 Daphnia to each one for an experiment. Pint sized Mason jars work really well for holding 10 Daphnia.
If you have 3 containers for each sample, then you will obtain enough data to determine if your results are statistically significant. Let me know if you need more information about statistics.
Now, what type of water samples are you planning to use? The protocol suggest using samples from a local parking lot, but the Daphnia test is a general all-purpose toxicity test that you can use to test any fresh water samples.
Here are some additional questions that you will need to know for this project.
1. What temperature is best for growing Daphnia and for doing your experiment?
2. What is your independent variable for this project?
3. What is your dependent variable?
4. What are you going to feed your Daphnia?
5. What is the best water to use for growing Daphnia?
6. Is there a better way to determine water toxicity?
Please post again in this topic if you have any other questions.