Calcium decline is an intensifying threat to freshwater ecosystems in the Canadian Shield. Many lakes in this region have also been contaminated with copper from industrial processes. Daphnia pulex is an important part of these ecosystems and has high calcium requirements, making it an ideal organism to study the effects of low calcium. Using the radioisotope 45Ca2+, this study focused on calcium uptake and how copper affects the uptake kinetics in D. pulex. Additionally, a series of separate experiments that used a novel screening device addressed how differences in calcium and copper concentrations affect survival. Copper decreased Km but not Vmax, which suggests competitive inhibition. Separately, low calcium and high copper both resulted in earlier mortality. Interestingly, low calcium with high copper resulted in longer survival compared to low calcium without copper. Implications of these results are discussed in the context of protocol development, physiological mechanisms, and government policy.