How Does Caffeine Affect the Heart Rate of the Daphnia?

My results and the graph indicate that as you add the caffeine to the daphnia, the eart rate of the daphnia increases for example the daphnia's heartbeat is 120 without caffeine, however when caffeine is added it is increased to 168. My graph shows a positive correlation and the error bars are also very small which shows that the results have a small range which suggests that my results are accurate and reliable. I think that the experiment was conducted well however there may be some ethical issues surrounding the fact that daphnias are also living species. Therefore, by using daphnias in these experiments may cause a risk for them as there would be little quantities of the species left. This would also affect other living organisms that feed on daphnias for their dietary needs therefore in the experiment we diluted the caffeine solution with distilled water to prevent the daphnia from dying and afterwards, we could put them back in their natural habitats. On the other hand, by doing this experiments it could potentially help us in the future. Also, another problem is that I may have miscounted the daphnias heartbeat due to human errors. However, as I repeated the experiment 3 times, it ensures me that the data is quite accurate. However, if I was to do the experiment again I would do more repeats to make sure the results are reliable and there would be less chance of human error. Also, I would use different concentrations of caffeine to get more accurate comparisons and to see how different concentrations may affect the daphnias heartbeat also. Overall, I think that my results are precise and distinct.