Hi Redicans ,
Welcome to Science Buddies!
I think you are doing this challenging, but excellent project:
https://www.sciencebuddies.org/science- ... #materials
The weight differences between the original sample and the final sample will probably be less than a gram, so it would be best to have a scale that can measure to 0.01 grams and even better to 0.001 grams. You need a gram scale because science project results should be reported using metric measurements.
If you boil a liter or quart of your well water to dryness, do you see a visible white powder in the pan? If not, then you could go ahead and use for this experiment. If you use the same water for all of your samples, it will be a controlled parameter, which is acceptable for a science project. If your water does have minerals in it, then it would be best to use distilled water to prepare the instant ocean.
When you set up this experiment, dry the mussel shells in an warm over (about 250 degrees F /121 degree C) until the weight of the sample does not change. When you finish the experiment, repeat this to make sure you are weighing only the shells, and not any extra water.
The experimental protocol recommends using containers that are list 0.5 L. To observe the maximum possible difference in the sample, use the largest container possible. The results depend on the solubility of the calcium carbonate mussel shells, and more will be able to dissolve in a larger volume of water.
Good luck on this project. Please let us know if you have any other questions.
Donna Hardy