Science Buddies: "Ask an Expert"

I’m trying to help my daughter analyze her project results & determine possibilities as to why her Science Fair Project failed. She chose to do the Something’s Fishy About That Fertilizer project from the Science Buddies website but it failed. The daphnia died almost immediately and the duckweed didn’t grow or multiply at all and in fact slowly died as well. She did the experiment twice & followed the procedures for the experiment exactly as written. We’re unable to try a third time because the project due date has been moved up to allow science fair winners at her school to attend the county’s Science Fair. Also, we used all the daphnia and duckweed we purchased from Carolina Biological Supply the first two times. Other than looking at whether the procedures were followed what can I recommend she look at as a reason her project failed. The distilled water we purchased had a ph of 5. Could that be a possibility they didn’t do well? Or the cold weather? Could the daphnia & duckweed have been in poor health due to cold temperatures during shipping? Also my daughter read that distilled water isn’t the water she should’ve used in an experiment using daphnia however that wouldn’t explain the duckweed doing so poorly? Any help you can give would be appreciated.

Moderator note: https://www.sciencebuddies.org/science- ... uatic-life

Sorry to hear this. It is admirable that you and your daughter are working on analyzing what might have gone wrong.

Carolina biological supply offers instructions on how to maintain Daphnia culture
https://www.carolina.com/teacher-resour ... cyFgWNL6Bx

This video provides tips for maintaining a healthy Daphnia culture
https://www.youtube.com/watch?v=oJIpTZoYF0E

Here is a link to a previous Ask an Expert thread that might help you with some troubleshooting for your project:
viewtopic.php?f=25&t=7695

pH of 5 might certainly be an issue. I did some research and this might be too acidic for Daphnia: https://www.ncbi.nlm.nih.gov/books/NBK2 ... 0and%208.5.

As far as duckweed is concerned, some sources cite a pH of 6-8 for optimal growth although studies do suggest that it can tolerate a pH of 5 (but may not have optimal growth). It also requires 10-12 hours of light daily.

https://www.wikihow.com/Grow-Duckweed
https://www.saps.org.uk/teaching-resour ... n-the-lab/

Shipping stress might have affected Daphnia. Given that its winter in some parts of the country, could that be an issue?

You are already analyzing the possible scenarios and it might be useful to look at this blog for what to do when things don't go as expected. Repeating the experiment, following procedures carefully, and then trying to troubleshoot is commendable
https://www.sciencebuddies.org/blog/sci ... e?from=AAE